THE RAT ADENINE PHOSPHORIBOSYLTRANSFERASE SEQUENCE SHOWS EVOLUTIONARYRATE VARIATION AMONG EXONS IN RODENTS

The complete genomic sequence of the rat APRT gene is described and co mpared with published mammalian sequences. The rat APRT gene organizat ion is typical of other rodent APRTs with five exons, one large intron of 993 bp, and three smaller introns averaging 145 bp. Because comple te sequences for mouse and Chinese hamster APRT are also known, it is possible to compare the evolutionary rates of change in the exons with those of the introns. The latter provide one possible estimate of und erlying rates of change. It is shown that the APRT exons have differen tial rates of evolution in rodents and have had a recent and rapid bur st of substitutions within the mouse lineage. Rates of change in the e xons do not appear to be strongly correlated with the rates of change in the introns.