intron-exon novice: minimum exon size??
rapulak at macc.wisc.edu
Wed May 17 22:24:53 EST 1995
David L. Haviland, Ph.D. writes:
>If memory serves, the murine C5-anaphylatoxin receptor is comprised of
>exons. Exon one contains only the 5' flanking sequence and the
>ATG - that's it. The rest of the coding (ORF) is on exon 2 which is 7
>downstream. Perhaps this "takes the cake" for the smallest exon, 3 bp!
Actually the first exon extends from the 5' end of the mRNA to the first
splice site and not just the nucleotides of the amino acid coding
region (often referred to as the coding sequence). There are several
genes that have "untranslated 5' exons" which have none of the coding
sequence; the first AUG is in the second exon. There are also a few
examples of genes that have final exons that are untranslated; translation
termination occurs in the penultimate exon (second last exon). However,
these are still exons even though they do not contain any coding sequence.
Rock Pulak rapulak at macc.wisc.edu
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