Short communication: Identification and characterization of multiple splicing forms of bovine prochymosin mRNA

Bovine prochymosin (bPC) is an inactive precursor of the milk clotting enzyme chymosin (EC 3.4.23.4), that is present in the abomasum of suckling calves. We investigated the pattern of bPC mRNA expression in the calf stomach tissues by RT-PCR assay and sequence analysis of cloned RT-PCR products. We identified multiple isoforms appearing due to alternative splicing of bPC mRNA. Alternative mRNA forms were generated by skipping one to four full exons within the bPC gene. Various splicing events resulted in seven bPC transcripts, which are 99, 114, 213, 237, 336, 351 and 450 nucleotides shorter compared to full-length mRNA. Analysis of amino acid sequences deduced from alternatively spliced mRNA sequences showed no amino acid transversions and no protein reading frame shift for any splice forms.