INSECT PROTEINS HOMOLOGOUS TO MAMMALIAN HIGH-MOBILITY GROUP PROTEINS-I Y (HMG-I/Y) - CHARACTERIZATION AND BINDING TO LINEAR AND 4-WAY JUNCTION DNA/

A chromosomal high mobility group (HMG) protein from an epithelial cel l line of Chironomus tentans (Diptera) was purified to homogeneity and chemically characterized. cDNA clones encoding this protein were isol ated and sequenced. The deduced amino acid sequence revealed a high si milarity to HMG protein I of mammalia. This insect protein has therefo re been designated cHMGI. It has a deduced molecular mass of 10,371 kD a and appears to be a product of a single gene copy. Similarly to mamm alian HMGI/Y proteins the insect cHMGI protein has three putative DNA- binding motifs with a sequence K/RXRGRP that are each encoded by one e xon of the gene. Using synthetic peptides we have shown that the first and the second moth are necessary for high-affinity binding of the pr otein to DNA. Protein cHMGI binds preferentially to AT-rich DNA with a half-saturation value of 1.1 nM. Both cHMGI and human HMGI proteins r ecognize specifically a four-way junction DNA. We have also purified a related protein with similar physico-chemical properties from Drosoph ila melanogaster It, cells. The identification and characterization of HMGI proteins in insects with polytene chromosomes and with the cytol ogic and genetic potential of Chironomus and Drosophila opens new poss ibilities for studying function(s) of this group of chromosomal protei ns.