Michael Bulmer

Codon usage and intragenic position

Data on codon usage bias in E. coli are re-examined with respect to intragenic position. The bias is less extreme near the beginning than in the rest of the gene, particularly in highly expressed genes. This is contrary to the previous finding that there is a linear decline in codon usage bias with position along weakly expressed genes but little or no change in bias along highly expressed genes. The effect is not confined to genes coding for proteins with leader peptides, as suggested earlier (Burns and Beacham, 1985). There is some evidence of a similar but smaller effect in yeast.

SELECTIVE DIFFERENCES AMONG TRANSLATION TERMINATION CODONS

The frequency of use of the three alternative translation termination codons has been examined in 165 Escherichia coli, 52 Bacillus subtilis and 106 Saccharomyces cerevisiae genes. Genes were first categorised according to their degree of bias in sense codon usage. In each species there is a very strong bias in favour of UAA (over UAG and UGA) in genes where sense codon usage is highly biased. This bias declines, principally with an increase in the use of UGA, in genes with lower sense codon bias. It appears that selection operating during translation may maintain the bias in stop codon usage. Such selection could result from the greater availability of UAA-cognate release factor(s), or from a lower frequency of translational readthrough at UAA.

Worker-queen conflict and sex ratio theory in social hymenoptera

SummaryThere is a conflict of interest between the queen and her worker-daughters in social hymenoptera over the ratio of investment in male and female reproductives. In the absence of worker-laying and inbreeding, the queen prefers a 1:1 (male : female) investment ratio, whereas the workers prefer a 1:3 ratio. Trivers and Hare (1976) suggest that the workers will win this conflict because they control the allocation of care to the young, but this argument ignores the fact that the queen controls the numbers of haploid and diploid eggs laid, and that the workers must operate within this constraint. We have investigated two theoretical models of this situation. We conclude that the queen may have considerable control over the investment ratio; two factors which may act in favour of worker control are a high cost of producing a new queen rather than a worker and the possibility of making a variable investment in a new queen with a concomitant variation in her fitness.