Post-transcriptional control of 26 k casein genes during lactogenesis in mouse mammary glands.

Stage-specific gene expression of 26 k casein, a major milk protein, was examined in mouse mammary glands. Mature mRNA (1.1 kb) with putative precursor RNA (k kb) was detected in the lactating gland. In contrast, the putative precursor RNA (5 kb) was also detected in the mammary glands of virgin or weaned mice when milk was not produced, although mature mRNA was not detected. The RNA transcripts showing heterogeneous size distribution were abundant in the nonlactating stages. These RNAs are shown to be transcribed in the opposite direction to the mature mRNA. These results suggest the regulation at the post-transcriptional level in the synthesis of caseins in the mammary glands.