Landstein D, Graves M V, Burbank D E, DeAngelis P, Van Etten J L
Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska, 68583-0722, USA.
Virology. 1998 Oct 25;250(2):388-96. doi: 10.1006/viro.1998.9388.
DNA sequence analysis of the 330-kb Chlorella virus PBCV-1 genome unexpectedly revealed several open reading frames which encode proteins that are homologous to sugar-manipulating enzymes including glutamine:fructose-6-phosphate amidotransferase (GFAT), UDP-glucose dehydrogenase (UDP-GlcDH), and hyaluronan synthase (HAS). PBCV-1 genes encoding the putative GFAT and UDP-GlcDH enzymes were expressed in Escherichia coli, and both recombinant proteins have the predicted enzyme activity in cell free extracts. These same two genes are transcribed early in PBCV-1 infection, and both genes are widespread among the Chlorella viruses. The products of the reactions catalyzed by these two enzymes are precursors in the biosynthesis of hyaluronan polysaccharide. Previous experiments established that, like the GFAT and UDP-GlcDH genes, the HAS gene is transcribed early and encodes a functional enzyme (DeAngelis, P. L., Jing. W., Graves, M. V., Burbank, D. E., and Van Etten, J. L. (1997) Science 278, 1800-1803). Interestingly, the predicted amino-acid sequences of the PBCV-1 GFAT and UDP-GlcDH enzymes are more similar to bacterial GFAT and UDP-GlcDH enzymes than to their eukaryotic counterparts. In contrast, the amino-acid sequence of the PBCV-1 HAS enzyme more closely resembles eukaryotic enzymes.
对330kb的小球藻病毒PBCV-1基因组进行DNA序列分析时，意外发现了几个开放阅读框，它们编码的蛋白质与糖类操纵酶同源，包括谷氨酰胺：果糖-6-磷酸酰胺转移酶（GFAT）、UDP-葡萄糖脱氢酶（UDP-GlcDH）和透明质酸合酶（HAS）。编码假定的GFAT和UDP-GlcDH酶的PBCV-1基因在大肠杆菌中表达，两种重组蛋白在无细胞提取物中均具有预测的酶活性。这两个相同的基因在PBCV-1感染早期转录，并且在小球藻病毒中广泛存在。这两种酶催化反应的产物是透明质酸多糖生物合成的前体。先前的实验表明，与GFAT和UDP-GlcDH基因一样，HAS基因也在早期转录并编码一种功能性酶（DeAngelis，P.L., Jing, W., Graves, M.V., Burbank, D.E., and Van Etten, J.L. (1997) Science 278, 1800 - 1803）。有趣的是，PBCV-1的GFAT和UDP-GlcDH酶的预测氨基酸序列与细菌的GFAT和UDP-GlcDH酶更相似，而与其真核对应物不太相似。相比之下，PBCV-1的HAS酶的氨基酸序列更类似于真核酶。
