furthermore , when the rna used in these experiments was prepared from cells with different levels of pyre expression , created by manipulations in their pyrimidine nucleotide supply , the frequency of transcription initiations at p1 and p2 was found to be constitutive , while only a pyrimidine regulated fraction of the mrna chains reached into the pyre gene .
C0035668
rna
C1158830
transcription initiations