Worm Breeder's Gazette 8(1): 35
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Karn et al. [PNAS 80, 4253 (1983)] recently published an intron boundary consensus sequence which is in need of some revision. The up- to-date consensus is shown below, along with the number of cases of deviation from the consensus at each position (out of a possible 14). The all-organism consensus is included for comparison [Breathnach and Chambon, Ann. Rev. Biochem., 50, 349 (1981)]. [See Figure 1] In C. elegans, the myosin, collagen, actin, and yolk protein gene families all provide examples of genes which contain an intron not present in one or more related genes. In previously analyzed cases it has not been possible to determine whether the intron is a late arrival into one of the genes or, alternatively, has been lost from the other. However, in one case an interesting aspect of the sequence leads us to the belief that a 49-base intron present in yp5 but not yp2 has been lost from the latter gene. The sequence indicates that the intron has been removed without alteration of the length of the surrounding coding regions. While the coding regions of yp5 and yp2 are about 70% homologous over most of their length, the regions around the intron are only 43% homologous. Interestingly, yp2 has apparently replaced the portions of the two exons surrounding the intron with a duplication of a region found in both genes about 30 bp 3' of the intron site. In this region, 18 out of 24 bp are homologous between the two apparently duplicated parts of yp2. [See Figure 1] Apparently, a duplication event resulted in formation of a larger exon from two smaller ones during the evolution of yp2. Mispairing and gene conversion may have been responsible for loss of this intron.