Tryptase 4, a new member of the chromosome 17 family of mouse serine proteases

Genomic blot analysis raised the possibility that uncharacterized tryptase genes reside on chromosome 17 at the complex containing the three genes tha t encode mouse mast cell protease (mMCP) 6, mMCP-7, and transmembrane trypt ase (mTMT). Probing of GenBank's expressed sequence tag data base with thes e three tryptase cDNAs resulted in the identification of an expressed seque nce tag that encodes a portion of a novel mouse serine protease (now design ated mouse tryptase 4 (mT4) because it is the fourth member of this family) . 5'- and 3'-rapid amplification of cDNA ends approaches were carried out t o deduce the nucleotide sequence of the full-length mT4 transcript. This in formation was then used to clone its similar to5.0-kilobase pair gene. Chro mosome mapping analysis of its gene, sequence analysis of its transcript, a nd comparative protein structure modeling of its translated product reveale d that mT4 is a new member of the chromosome 17 family of mouse tryptases. mT4 is 40-44% identical to mMCP-6, mMCP-7, and mTMT, and this new serine pr otease has all of the structural features of a functional tryptase. Moreove r, mT4 is enzymatically active when expressed in insect cells. Due to its 1 7-mer hydrophobic domain at its C terminus, mT4 is a membrane-anchored tryp tase more analogous to mTMT than the other members of its family, As assess ed by RNA blot, reverse transcriptase-polymerase chain reaction, and/or in situ hybridization analysis, mT4 is expressed in interleukin-5-dependent mo use eosinophils, as well as in ovaries and testes. The observation that rec ombinant mT4 is preferentially retained in the endoplasmic reticulum of tra nsiently transfected COS-7 cells suggests a convertase-like role for this i ntegral membrane serine protease.