REGULATORY SEQUENCES AND A NOVEL GENE IN THE MSP (GP63) GENE-CLUSTER OF LEISHMANIA-CHAGASI

The surface protease GP63 of Leishmania chagasi is encoded by a cluste r of more than 18 tandem major surface protease (msp) genes belonging to three classes (mspL, mspS, mspC). mspL and mspS transcripts are dif ferentially expressed during parasite growth. RNAs from mspS genes pre dominate during stationary phase, the time when parasite virulence and GP63 expression are maximal. We hypothesized that the unique regions downstream of mspS genes contain signals important for gene expression . The 2.8 kb region between tandem mspS genes was found to contain an 882 bp open reading frame designated mag. Copies of mag were found dow nstream of all mspS genes in the cluster, mag hybridized faintly to ba nds on Northern blots and a fully processed mag cDNA was identified in a promastigote cDNA library, providing evidence that mag genes are ex pressed at low levels. Similar to mspS RNAs, the abundance of mag RNAs was greater in stationary phase than logarithmic phase organisms, alt hough mag RNAs were less abundant than mspS RNAs throughout growth. No rthern blots and enzyme assays of promastigotes containing plasmid con structs in which the beta-galactosidase gene was followed by sequences between mspS coding regions, either with or without mag and its downs tream sequences, suggest these regions have several regulatory effects accounting for the growth-associated changes in mspS expression. (C) 1998 Elsevier Science B.V. All rights reserved.