Mosaic structure and mRNA precursors of uteroglobin, a hormone-regulated mammalian gene

The synthesis of uteroglobin in the rabbit uterus is induced by progesterone and is repressed by estrogen which has an over-riding effect over the inducer. The dual hormonal control system offers an excellent model for studying hormonal regulation of mammalian gene expression. Using a full-length uteroglobin cDNA clone as a specific hybridization probe, recombinant lambda phages containing the entire chromosomal uteroglobin gene have been isolated from a rabbit genomic DNA library. Electronmicroscopic analysis of hybrid molecules formed between the chromosomal uteroglobin gene and uteroglobin mRNA indicated the presence of 2 intervening sequences within this gene. The mosaic structure of the uteroglobin gene has been substantiated by detailed restriction mapping and Southern hybridization. The gene is 3.0 kilobases in length to code for a mature mRNA of 465 nucleotides. Northern hybridization of poly(A)-containing RNA from 4-day-pregnant rabbit uterus with the full-length cDNA clone revealed the presence of uteroglobin mRNA precursors. The size of the largest precursor RNA species detected by the cDNA clone is the same as the entire chromosomal uteroglobin gene. The fidelity of the precursor RNAs was established by their ability to hybridize with specific intervening sequence probes. Thus the entire uteroglobin gene is expressed into primary RNA transcripts, which are subsequently processed into mature mRNA molecules by splicing.