The following abstract, submitted in January 1994, illustrates the general difficulty that was experienced getting the ideas on these pages past the peer-review gate. Sometimes there were delays of several years. Editors also tend to redate revised papers which gives the impression that publication in their journals is rapid. The paper, of which this is the abstract, did not appear until late in 1995. Note reference to a paper submitted to Nucleic Acids Research which eventually had to be submitted elsewhere. The paper submitted to the Journal of Theoretical Biology did not surface until 1996.

Abstract: Proc. Can. Fed. Biol. Socs. 37, 152 

(Presented in Montreal in June 1994).

PERCENTAGE G+C DETERMINES 

FREQUENCIES OF COMPLEMENTARY 

TRINUCLEOTIDE PAIRS: IMPLICATIONS FOR 

SPECIATION
. D. R. Forsdyke. Department of Biochemistry, 

Queen's University, Kingston, Ontario K7L3N6

To an approximation Chargaff's rule applies to long sequences of single stranded DNA. It follows that complementary oligonucleotides are present in approximately equal frequencies. Thus a plot of the frequencies of 32 trinucleotides against those of their 32 complements is rectilinear with an intercept close to the origin (Prabhu, 1993. NAR 21,2797). I have compared the frequencies of trinucleotides in long sequences and their shuffled counterparts. Trinucleotides fall into 4 main frequency groups: (i) WWW, (ii) WWS+WSW+SWW, (iii) SSW+SWS+WSS, and (iv) SSS. Among the 32 complementary trinucleotide pairs there is a hierarchy of frequencies which is influenced both by percentage G+C (not affected by shuffling the order of bases) and by primary sequence. It is proposed that evolutionary pressures select for sequences with complementary oligonucleotides in close proximity, thus creating the potential to form stem-loops. These are dispersed throughout genomes and are rate-limiting in recombination (Tomizawa,1984. Cell 38, 861; Forsdyke, J. Mol. Evol. submitted). Individual species have fine-tuned their stem-loop forming potential to avoid recombination with other species. As a consequence we see today that similar species in similar environments may differ greatly in G+C percentages (Forsdyke, J. Theor. Biol. and Nucleic Acids Res. submitted).

Supported by the MRC of Canada.

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