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Characterization of nuclear basic proteins in sperm and erythrocytes of vertebrates Su, Hua Wei

Abstract

I have examined the arginine-enriched nuclear basic proteins (NBPs) that condense chromatin in two kinds of transcriptionally inactive, terminally differentiated cells of non-mammalian vertebrates: sperm and erythrocytes. I have focused on the characterization of sperm nuclear basic proteins (SNBPs) in teleost fish and erythrocyte nuclear basic proteins (ENBPs) in reptiles and birds by electrophoresis, high pressure liquid chromatography and amino acid analysis to ask: 1) Is internal fertilization a constraint on the diversity of SNBPs seen in teleost fish and frogs? 2) Is bird linker histone H5 also present in alligator erythrocyte nuclei? I have found that internally fertilizing Xiphophorus helleri guentheri (swordtail), Xiphophorus maculatus (platyfish), Poecilia reticulata (guppy), Poecilia picta (guppy) and Cymatogaster aggregata (shiner perch) all contain protamines as their SNBPs. Amongst frogs, there is a sporadic reversion from protamines in the primitive, internally fertilizing frog Ascaphus truei, to sperm histones among several more advanced, externally fertilizing frogs (Kasinsky et al., 1999). This parallels a simplification of elongated introsperm to more rounded ectaquasperm in advanced neobatrachians that is regarded as a secondary reversion to external fertilization (Lee and Jamieson, 1992). However, characterization of SNBPs from the internally fertilizing neobatrachian frog Eleutherodactylus coqui shows the presence of four protamines. These results favor the hypothesis (Kasinsky, 1989) that fish and frogs with internal fertilization tend to select arginine-rich protamines as their SNBPs rather than sperm histones, whereas external fertilization is compatible with protamine-to-histone reversions in some advanced frogs. Is linker histone H5 unique to bird erythrocyte nuclei? H1°, another differentiationspecific linker histone in vertebrates, is not erythrocyte-specific. I have characterized ENBPs from Ictalurus punctatus (catfish), Rana catesbeiana (bullfrog), Chelonia mydas (sea turtle), Alligator mississippiensis (alligator), and Gallus gallus (chicken), as well as possible NBPs in the condensed nucleus of mouse normoblasts, the precursors of mature enucleated red blood cells. Alligator ENBPs appear to contain a linker histone H1°/H5 which is midway in the evolutionary trend from H1° to H5. This is consistent with the fact that alligators have a higher average blood pressure than sea turtles but much lower than in birds.

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