Moss - What genes cant do - 2003 (522929), страница 18
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As in other disciplines, it is throughthe circulation of the information discourse that their objects of study were(separately) reconfigured anew, and then emerged, not entirely surprisingly, withsome parallel features. And it is this simultaneous dematerialization of bothlanguage and life that soon formed the conditions of possibility for envisioningthe word (information of the DNA sequence) as the origin of self-organization,the ontological unit of life and evolution (Kay 2000).Gamow’s first response to the Watson and Crick double helix was toapproach the Navy’s Bureau of Ordinance, which had deciphered andbroken Japanese code, with lists of amino acids and DNA bases to putinto its deciphering computer.
Gamow reported that “after two weeksthey informed me there is no solution” (in Kay 2000). Gamow (1954)The Rhetoric of Life and the Life of Rhetoric65quickly offered a solution of his own, known as “the diamond code,”which entailed a direct physical translation between DNA and aminoacids. The diamond code consisted of all the unique arrangements of thefour DNA bases organized into a diamond shape. As it happens thereare exactly 20 diamond-shaped configurations that correspond numerically with the fact of 20 amino acids. This became known as the “magictwenty.” Gamow’s idea was that each diamond configuration, defined bythe arrangement of four bases, one at each of the vortices, resulted in 20unique rhomb-shaped holes into which each of the amino acids wouldfit. Gamow’s model described an unmediated direct physical relationshipbetween DNA and protein.
Indeed, had Gamow’s model held up, thenotion of a direct translation between DNA and protein sequence wouldhave to be granted a certain literal legitamacy. That Gamow’s diamondmodel could not be empirically supported is of prime importance incritically examining the rhetorical trajectory of molecular biology.Gamow’s diamond quickly met with criticism from the likes of LinusPauling, Erwin Chargaff, Francis Crick, and Martin Yc̆as, whose thinking relied upon, amongst other things, inferences made on the basisof Fred Sanger’s newly sequenced insulin. As a visiting professor atBerkeley in the fall of 1954, Gamow elicited the interest of Caltechluminaries Delbrück, Alex Rich, and Richard Feynman with his desireto pursue the coding problem.
The role of RNA as an intermediate inprotein synthesis had gained favor at Caltech in the context of an atmosphere in which there was already an appetite for using the most sophisticated mathematical methods and computer resources available andapproaching the problem as one akin to breaking enemy code. Gamowformalized the group as the “RNA Tie Club,” consisting of 20 members,each issued a diagrammed tie, designed by Gamow, representing one ofthe amino acids (Kay 2000).Approaching the coding problem as one of analyzing a language meantlooking for the kinds of restrictions which are characteristic of naturallanguages. The distribution of letters in words are not random but followrules or patterns that pertain jointly to all, or most, of the words in alanguage.
Many such restrictive (overlapping) codes were proposed bysome of the preeminent theorists of the day (von Neumann, Weiner,Gamow, Rich, Crick, and Delbrück) using the Los Alamos Maniac66Chapter 2computer for assistance. If codes were fully overlapping then, forexample, a sequence of ABCD would code for two amino acids, onebased on ABC and the other on BCD. Being fully overlapping avoids anyproblem of punctuation because every base is the beginning of a newcodon, but it will also place restrictions on which amino acids canprecede or succeed any particular amino acid as each codon must sharetwo-thirds of its sequence with the codons that come before and after it.Not every amino acid can precede or succeed any other amino acid.Models of overlapping codes with their attendant restrictions could beexamined theoretically and with reference to known sequences of aminoacids and DNA:The results were negative. In spite of the strong inter-symbol restrictions inthe proposed codes, both the artificial sequences constructed based uponthem and the naturally occurring sequences produced a random amino acid distribution.
Rather than question their guiding premise that the code was overlapping, or more fundamentally, that the scheme was in fact, a language likecode, the team inferred that the method employed was not sensitive enough (Kay2000).The efforts of the RNA Tie Club continued for 5 years, producingmany hypothetical codes but little biological accomplishment. While theheuristics of “nucleic-acid sequence as language” did not prove to be biologically fruitful, it left an enduring legacy at the level of the speech-styleused to describe and conceptualize molecular-level biology.Rhetorically fashioned by information theory, DNA emerged as a closecousin of language and encryption.
The random distribution of elementsin both DNA and protein contravene the expectations for a language tobe overlapping and restrictive, yet the insinuation of semantic propertiesin the DNA/RNA sequence continued to accrue. In approaching the challenge of a nonoverlapping code it was pointed out that any nonoverlapping code would have to account for how at any given locus “a basesequence read one way makes sense, and read the other way makes nonsense” (Yc̆as 1969). DNA strands, to this day, are distinguished as senseand nonsense, and not only does template-based polymer synthesis countas reading but also a complex array of enzyme-based proofreading mechanisms have become part of the canon as well.
Another enduring pieceof language metaphor was introduced by way of an empirically unsuc-The Rhetoric of Life and the Life of Rhetoric67cessful attempt to resolve the challenge of a nonoverlapping code andthe absence of punctuation marks.Given the fact of an ongoing sequence of nucleic acid bases which areread three at a time, how is it possible for them to be read in only oneregister, i.e., how is the start and stop of each triplet distinguished? Crick,Orgel, and Griffith offered their scheme for a comma-free code in 1956.The solution they proposed illustrates the influence of the linguisticmetaphor. Their solution consists of partitioning all the possible codons(sequences of three) into those that have “meaning” and those that don’t.The key to this partition is to locate all and only those codons that whentaken together can be juxtaposed without creating the possibility of ameaningful codon existing by overlap.
So, for example, for ABC andDAB to meaningful, it would require that BCD and CDA, as well as ABAand BAB, could not be. All the meaningful codons would then constitute a “dictionary” by their terms. In this way a sequence would be readunivocally and without the need for punctuation.
Although this did notprove to be the solution to the comma-free code problem, the rhetoricof textuality grew further and prospered.The coding problem, that is, the basis by which RNA/DNA serves asa specific resource in the biosynthesis of proteins, was solved entirelyoutside of the organizational associations of Caltech and the RNA TieClub, as well as the whole of the information-theoretical apparatus.Marshall Nirenberg and Heinrich Matthaei at the National Institutes ofHealth solved it empirically using methods of wet biochemistry.
Butdespite the fruitlessness of the efforts of Gamow and his theoreticallyminded collaborators, their stylization of the relationship between DNAand everything else in terms of linguistic and crytographic metaphorswas successful.Listening to the WordsFrom Schrödinger’s code-script to the fashioning of DNA in terms oftranslation, sense and nonsense, reading and reading frames, meaning,dictionaries, libraries, and the like, the imputation of semantic contenthas followed its own logic and served to set the stage for subsequentemerging perceptions and interpretations in the discipline. I have68Chapter 2suggested that it would have made a difference if something likeGamow’s diamond code—in which DNA and proteins would have interfaced in close physical register—had proven to be warranted.
Translation then, in its immediate specification, might have become innocuousin its victory, progressively taking on more of the character of a technical term denuded of its broader resonances. But as the characterizationof molecular interactions has evidenced greater complexity and multidirectionality of effect, the impact, if anything, on the semanticizing idiomhas been to cut it more slack, to allow it the opportunity to veer off inits own direction with but a fluttering empirical tether. If the rhetoricaldimension of the history of the gene has to some extent charted its owncourse, then an attempt such as Doyle’s to examine the “rhetorical transformations of the life sciences” is warranted.As in the cases of a gestalt-switch experience, perceiving the duck orthe rabbit, for example, the use of a metaphor to structure a perceptualfield organizes the relationship between foreground and background.Doyle is especially concerned with making manifest what assumptionsare marshaled together as the necessary background correlate of structuring a field by way of a certain rhetorical trope.
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