RAPID COMMUNICATION ZIPGRAM zy RELEASE OF DNA TEMPLATE RESTRICTIONS IN RABBIT SPERMATOZOA AND RAT LIVER NUCLEI (1) BARRY R. ZIRKIN, ADELE BOISON, W. D. W. HESTON, AND DONALD S. COFFEY Departments o f Population Dynamics and Pharmacology and Experimental Therapeutics, The Johns Hopkins University, Baltimore, Maryland 21205 ABSTRACT The effects of disulfide reduction on DNA template activity of rabbit sperm and rat liver nuclei are compared. After treatment of rabbit spermatozoa with 5 mM dithiothreitol and 1% Triton X-100 for 90 minutes a t room temperature, sperm nuclei decondense and nu- clear template restrictions for DNA synthesis are released. By con- trast, similar thiol treatment of isolated rat liver nuclei fails to release DNA template restrictions. icant difference i n the control of template activity i n mammalian sperm and somatic cell nuclei. These results suggest a signif- In a recent study (Heston e t a1 , '75), we demonstrated that certain acidic polymers were capable o f releasing nuclear template restrictions for DNA syn- thesis in rabbit spermatozoa, but only if the spermatozoa were b r i e f l y exposed to disulfide reducing agents prior to their incubation with acidic polymers. In these experiments, neither the acidic polymers nor the thiol reagents by themselves stimulated DNA temp1 ate activity. I n the present study, we examine the effects of extensive reduction of disulfide bonds on sperm DNA template activity and nuclear morphology, and compare the results to those obtained with similarly treated, isolated rat liver nuclei. MATERIALS AND METHODS Fresh ejaculates o f rabbit spermatozoa were zy ob- tained from New Zealand White rabbits with an artificial vagina. ulates were pooled, washed twice with ice-cold Tris (50 mM, pH 7.4) o r TM Several ejac- (50 mM Tris; 5 mM MgC12; pH 7.4) buffer, and resuspended i n ice-cold buffer. A portion of this sperm suspension was treated with 1% Triton X-100 and 5 mM 283