Identification of a novel first exon of prolactin receptor gene expressed in the rat brain.

A novel first exon, E1(4), whose sequence was distinct from those of the three known first exons, E1(1), E1(2), and E1(3), of the rat PRL receptor (PRL-R) gene was identified by cDNA cloning for the 5'-end region of PRL-R mRNA expressed in the rat brain. Sequence analysis revealed the presence of two different length E1(4) cDNAs. The longer cDNA contained the 243-bp E1(4) sequence, and the shorter cDNA lacked the 139-bp sequence at the 5'-end of the longer one.