DNA CONDENSATION BY THE RAT SPERMATIDAL PROTEIN TP2 SHOWS GC-RICH SEQUENCE PREFERENCE AND IS ZINC DEPENDENT

Transition protein-2 (TP2), isolated from rat testes, was recently sho wn to be a zinc metalloprotein. We have now carried out a detailed ana lysis of the DNA condensing properties of TP2 with various polynucleot ides using circular dichroism spectroscopy. The condensation of the al ternating copolymers by TP2 (incubated with 10 mu M ZnSO4), namely, po ly(dG-dC). poly(dG-dC) and poly(dA-dT). poly(dA-dT), was severalfold h igher than condensation of either of the homoduplexes poly(dG). poly-( dC) and poly(dA). poly(dT) or rat oligonucleosomal DNA. Between the tw o alternating copolymers, poly(dG-dC). poly(dG-dC) was condensed 3.2-f old more effectively than poly(dA-dT). poly(dA-dT). Preincubation of T P2 with 5 mM EDTA significantly reduced its DNA-condensing property. I nterestingly, condensation of the alternating copolymer poly(dI-dC). p oly(dI-dC) by TP2 was much less as compared to that of poly(dG-dC). po ly(dG-dC). The V8 protease-derived N-terminal fragment (88 aa) condens ed poly(dA-dT). poly(dA-dT) to a very small extent but did not have an y effect on poly(dG-dC). poly-(dG-dC). The C-terminal fragment (28 aa) was able to condense poly(dA-dT) . poly(dA-dT) more effectively than poly(dG-dC). poly(dG-dC). These results suggest that TP2 in its zinc-c oordinated form condenses GC-rich polynucleotides much more effectivel y than other types of polynucleotides. Neither the N-terminal two-thir ds of TP2 which is the zinc-binding domain nor the C-terminal basic do main are as effective as intact TP2 in bringing about condensation of DNA.