Regulation of gene expression in eukaryotes occurs at three levels; transcription, post-transcription and translation. In an attempt to better understand the molecular mechanisms involved in post-transcriptional regulation, we will examine the processing of the mRNAs coding for bovine pre-prolactin (pre-PRL) and pre-growth hormone (pre-GH). Both nuclear and cytoplasmic forms of these two mRNAs will be studied in normal and transformed bovine pituitary cells in culture. Complementary double-stranded DNA to pre-PRL and pre-GH mRNA sequences will be cloned in the EK-2 host, E. coli X1776. Pre-PRL and pre-GH specific DNA recovered from these clones will be used to prepare affinity columns for the isolation of nuclear and cytoplasmic mRNA sequences. Methylation patterns of pre-PRL and pre-GH mRNA will be determined in both normal and transformed bovine pituitary cells. Inhibitors of mRNA methylation will be used to block the methylation of pre-PRL and pre-GH mRNA sequences and the effect of these inhibitors on mRNA processing will be determined. Our long term goal is to clarify the role of post-transcriptional methylation and 5'-terminal capping in mRNA processing.