Fig. 9. Relationship between expression levels and use of termination codons UAA and UGA in short genes in E.coli. All 342 short genes smaller than 100 codons were analysed for the distribution of the termination codons UAA and UGA. The gene expression levels were grouped according to their codon adapation index, where a high value reflects a high level of expression. The genes were divided into three groups with low (<0.3), medium (0.3–0.5) or high (>0.5) CAI values (Sharp and Li, 1987). The data were obtained from the E.coli genome bank of Wisconsin University (http://www.genome.wisc.edu/pub/analysis/).