DIFFERENTIAL SPLICING OF THE GROWTH HORMONE-RELEASING HORMONE GENE INRAT PLACENTA GENERATES A NOVEL PRE-PROGHRH MESSENGER-RNA THAT ENCODESA DIFFERENT C-TERMINAL FLANKING PEPTIDE

We have isolated and characterized a novel rat placental pre-proGHRH m RNA (pre-proGHRH-2 mRNA). This mRNA is generated by an alternative spl icing process which results in the presence of an additional exon of 1 56 bp (designated exon 4.5) located between exons 4 and 5 of the previ ously reported hypothalamic and placental pre-proGHRH mRNA (pre-proGHR H-1 mRNA), Since the sequences encoding mature GHRH are included withi n exons 3 and 4, the processing of pre-proGHRH-2 would not affect the synthesis of mature GHRH but would generate a C-terminal peptide (desi gnated GCTP-2) different from that previously reported in the hypothal amus and placenta (GCTP-1), The putative GCTP-2 has 64 amino acids, an d the first 18 N-terminal residues are identical to those present in G CTP-1 (30 amino acids long), Pre-proGHRH-2 mRNA has not been detected in the hypothalamus.