LYSOZYME-ENCODING BOVINE CDNAS FROM NEUTROPHILE GRANULOCYTES AND MAMMARY-GLAND ARE DERIVED FROM A DIFFERENT GENE THAN STOMACH LYSOZYMES

cDNA copies of a bovine lysozyme (bLys)-encoding gene (Lys) were isola ted from libraries specific for granulocytes, as well as the lactating mammary gland. Analysis of each of the longest Lys-specific cDNA inse rts revealed nucleotide sequence identity over the entire overlap of 1 418 bp. Incomplete at the 5' end, the combined sequence codes for 11 o f the 18-amino-acid (aa) Lys leader peptide and 130 aa residues of the mature Lys. Similar to mouse and human Lys from blood cells, the enco ded protein contains one aa residue more (pro(103)) than any of the bL ys derived from stomach. Furthermore, unlike any of the known bLys gen es, our sequence reveals the copy of a bovine retroposon element in th e 3' untranslated region (UTR) of the mRNA approximately at the same p osition where an Alu-retroposon element resides within the human copy of the gene. As a further distinction from bLys expressed in stomach, we identified a segment within the 3' UTR of the mRNA which is conserv ed between the bovine and human blood cell variants of the Lys, but do es not have significant sequence homology to any of the bovine lysozym e genes known so far. By sequence comparisons, we present evidence tha t this segement has been deleted during evolutionary divergence of the stomach Lys. Hence, we describe the sequence of a heretofore unknown bLys, being expressed in granulocytes. Bearings of our observations on the understanding of Lys evolution are discussed, as well as the poss ibility that the product of this gene may be responsible for the funct ional Lys activity in bovine milk.