Inhibition of nuclear envelope reconstitution in Xenopus interphase egg extract by hemin

Addition of hemin to the nuclear reconstitution system of Xenopus interphas e egg extract using sperm head chromatin resulted in abnormal pseudonuclei exhibiting flattened membrane patches randomly distributed both on the surf ace and inside the nuclei. The structures that resembled nuclear pores were observed on these flattened membrane patch structures. Although the nucleo some structure was formed as revealed by the micrococcal nuclease digestion , the B-type lamin uptake into the nuclei was inhibited by hemin. Using hem inagarose affinity chromatography, we isolated several hemin-binding protei ns from fully reconstituted pseudonuclei. Some of the hemin-binding protein s bound concanavalin A (Con A). Comparison of hemin-binding proteins with t hose isolated from both fractions of supernatant and pellet separated by hi gh speed centrifugation of the egg extract showed that the hemin-binding pr oteins of pseudonuclei were supplied from both fractions. The uptake of nuc lear hemin-bindmg proteins did not occur in the incompletely reconstituted nuclei resulting from addition of excess sperm chromatin to the system. The se results suggest that the hemin-binding proteins participate in the late steps of nuclear reconstitution during formation of the nuclear envelope.