The nucleotide sequence of tomato ringspot nepovirus (TomRSV) RNA1 has been determined. TomRSV RNA1 is 8214 nucleotides in length, excluding the 3' poly(A) tail, and contains a single long open reading frame (ORF) of 6591 nucleotides beginning at the first AUG codon at nucleotide position 78. This ORF accounts for 80 % of the RNA1 sequence and would give rise to a polyprotein with a predicted molecular mass of 244 kDa. Amino acid sequence comparisons between portions of the TomRSV RNAl-encoded polyprotein and proteins encoded by several members of the picornavirns superfamily have provided information concerning the genomic organization and putative functions of TomRSV-encoded proteins. The putative TomRSV protease retains a conserved histidine residue present in the proteases encoded by members of the como-, poty-and poliovirus groups which is thought to be involved in dipeptide cleavage site recognition. Interestingly, this histidine residue is replaced by a leucine in the proteases of other sequenced nepoviruses. This suggests that the TomRSV protease shares dipeptide cleavage site specificity with that of como-, potyand picornaviruses rather than the other nepoviruses.
Pancreatic DNase requires both Ca2+ and Mg2+ for its activity as measured by formation of an activated DNA template for in vitro DNA polymerase alpha assay and by the hyperchromic shift. Mn2+ can partially satisfy the Mg2+ requirement of the DNase for activation of DNA but the resulting template is only 50% as active in the DNA polymerase assay. When precautions are taken to avoid divalent ion contamination, pancreatic DNase is not active in the presence of Ca2+ or Mg2+ alone. analysis of the DNA by sucrose gradient centrifugation shows that only in the presence of Ca2+ plus Mg2+ or Mn2+ does pancreatic DNase produce extensive strand breaks in the DNA. The activated DNA template that yields maximal DNA polymerase activity is low molecular weight material of 30,000 to 50,000 daltons.
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