Unformatted text preview: expression in C. elegans: A comprehensive example Computer programs search for possible exons by looking for strings of codons uninterrupted by nonsense codons. Look for splice donor and acceptor sites to identify introns. C. elegans genome contains roughly 19,000 genes. 15% encode worm's genes or proteins. Landmarks in a callogen gene of C. elegans and comparison of DNA and mRNA sequences
Fig. 8.26 Mutations in a gene's coding sequence can alter the gene product. Silent mutations do not alter amino acid specified. Missense mutations replace one amino acid with another. Nonsense mutations change an amino-acid-specifying codon to a stop codon. Frameshift mutations result from the insertion or deletion of nucleotides within the coding sequence. Mutations outside of the coding sequence can also alter gene expression. Promoter sequences Termination signals Splice-acceptor and splice-donor sites Ribosome binding sites Fig. 8.27 c Mutations in genes encoding the molecules that implement expression may affect transcription, l mRNA splicing, or translation.
Usually lethal Mutations in tRNA genes can suppress mutations in protein-coding genes. Nonsense suppressor tRNAs Nonsense suppression (a) Nonsense mutation that causes incomplete nonfunctional polypeptide (b) Nonsensesuppressing mutation causes addition of amino acid at stop codon allowing production of full length polypeptide. Fig. 8.28...
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