5'-RACE PCR of mRNA for three taxon-specific crystallins: for each gene one promoter controls both lens and non-lens expression.

Gene recruitment of enzyme crystallins is a novel process in molecular evolution in which genes for some metabolic enzymes acquire extremely high expression in lens without prior gene duplication. Using the RACE method, the 5' end of the mRNAs for duck lens delta 1-, argininosuccinate lyase/delta 2- and lactate dehydrogenase-B/epsilon-crystallin has been amplified from lens and non-lens tissues and sequenced. In all three cases the major transcription start sites were identical in lens and in other tissues. This suggests that for these three genes, and in contrast to at least one other example, gene recruitment does not require the presence of alternative tissue-preferred promoters.