an examination of steady-state rna levels in cells carrying these mutations and a comparison with similar data from other dhfr mutants ( a. m. carothers , r. w. steigerwalt , g. urlaub , l. a. chasin , and d. grunberger , j. mol . biol. , in press ) showed that translation termination mutations in any of the internal exons of the gene gave rise to a low-rna phenotype , whereas missense mutations in these exons or terminations in exon 6 ( the final exon ) did not affect dhfr mrna levels .
C0007634
cells
C0015295
exon