Tao J, Ginzberg I, Koltin Y, Bruenn J A
Department of Biological Sciences, SUNY, Buffalo 14260.
Mol Gen Genet. 1993 Apr;238(1-2):234-40. doi: 10.1007/BF00279552.
Double-stranded RNA viruses of Ustilago maydis encode secreted killer toxins to which other cells of the same species and closely related species are sensitive. KP6 toxin consists of two polypeptides, alpha and beta, produced from a single precursor preprotoxin. In this work, we cloned complementary DNA for the toxin-encoding segment of two of the KP6 nonkiller mutants NK3 and NK13 that secrete the beta and alpha polypeptides, respectively. Both sequence analysis of the cDNA clones and in vitro translation of the toxin-encoding double-stranded RNAs showed that both mutants can produce full-length preprotoxins. Cys51 in alpha is converted to Arg in NK3 and Thr25 and Lys42 in beta are changed to Pro and Arg, respectively, in NK13. Although alpha and beta are encoded in a single prepropolypeptide, only the beta polypeptide is secreted by NK3 and only the alpha polypeptide is secreted by NK13. This differential expression of peptides from one precursor is a unique phenomenon. Neither of the nonsecreted polypeptides accumulated in the cytosol. The possible effects of these mutations on preprotoxin folding and their consequences for toxin secretion are discussed.
玉米黑粉菌的双链RNA病毒编码分泌型杀伤毒素，同一物种和近缘物种的其他细胞对该毒素敏感。KP6毒素由α和β两条多肽组成，由单一前体前原毒素产生。在这项研究中，我们克隆了两个KP6非杀伤突变体NK3和NK13毒素编码片段的互补DNA，它们分别分泌β和α多肽。cDNA克隆的序列分析以及毒素编码双链RNA的体外翻译均表明，这两个突变体都能产生全长前原毒素。在NK3中，α中的Cys51转变为Arg，在NK13中，β中的Thr25和Lys42分别变为Pro和Arg。尽管α和β由单一前原多肽编码，但NK3仅分泌β多肽，NK13仅分泌α多肽。来自一个前体的这些肽的差异表达是一种独特的现象。两种非分泌型多肽均未在细胞质中积累。讨论了这些突变对前原毒素折叠的可能影响及其对毒素分泌的后果。
