Worm Breeder's Gazette 11(3): 48
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.
In order to find out more about lin-14, we decided to sequence it. We sequenced 8 cDNAs and the corresponding genomic regions. The gene spans more than 21 kb, and has 13 exons. Two alternatively spliced transcripts were observed in this set of cDNAs and verified by RNase protection. One transcript splices exons 1, 2, and 3 to exons 5 to 13, while the other transcript splices exon 4 to exons 5 to 13. Exon 4 is in the large intron (12 kb) between exons 3 and 5. Both transcripts are approximately 3.3 kb, which is close to the observed size from Northern blots (3.5 kb). The precise 5' end of the messages has not yet been determined. The 3' end has a 1.6 kb untranslated region. Two gain-of-function mutations (n355 and n536) have been sequenced and found to be localized in this 3' untranslated part of both transcripts. The levels of n355 and n536 mRNA show the same developmental profile as wild-type mRNA, but the lin-14 protein stays abnormally high in these mutants. Thus the 3' untranslated region of the transcript confers post-transcriptional control to lin-14.[See Figure 1] The two transcripts code for two proteins (solid boxes, first figure) with distinct amino-termini. No homology to any other protein has been found. There is a basic region (residues -420 to 445; basic residues shown bold in second figure) that might be involved in DNA or RNA binding. The levels of lin-14 protein declines rapidly from mid- L1 to L2. This suggests that the protein could be unstable, and consistent with this idea, PEST sequences, which are thought to mediate rapid degradation of proteins, can be found in several places ( shown italicized). The lin-14B transcript probably encodes the lin-14B gene activity as described by Ambros and Horvitz (1987), see abstract by Wightman et al. The loss-of-function mutation n838 is a point mutation that changes an Alanine to a Threonine. This mutation is genetically lin 14a-b+, but the amino acid change is in an exon common to both transcripts. [See Figure 2]
