Vickerman M M, Sulavik M C, Nowak J D, Gardner N M, Jones G W, Clewell D B
Department of Microbiology and Immunology, School of Medicine, University of Michigan, Ann Arbor 48109-0620, USA.
DNA Seq. 1997;7(2):83-95. doi: 10.3109/10425179709020155.
Streptococcus gordonii has an extracellular glucosyltransferase (GTF) that polymerizes the glucose moiety of sucrose to form both water-soluble and water-insoluble glucans. Whereas multiple gtf genes have been identified in strains of mutans streptococci and Streptococcus salivarius, a single gene, designated gtfG, encodes the GTF of S. gordonii Challis. gtfG is also unique among the characterized gtfs in that it has a described regulatory determinant, rgg. Furthermore, the GTF activity in S. gordonii undergoes reversible phase variation between high and low levels. In order to gain insight into this novel GTF system, the nucleotide sequence of gtfG was determined and found to consist of a 4,734 base pair open reading frame encoding a protein with a deduced molecular weight of ca. 174,000. gtfG was similar to other sequenced gtfs with a conserved signal sequence followed by a ca. 600-bp region distinctive for gtfG, a conserved region encoding a putative catalytic active site and a series of six direct repeats in the carboxyl terminal region implicated in glucan binding. Although comparison of gtfG to other gtfs did not show a basis for the primer-independence of the encoded enzyme or the nature of the glucan products, the gtfG sequence data provide an important basis for further studies of these enzymes.
戈登氏链球菌具有一种细胞外葡糖基转移酶（GTF），它能使蔗糖的葡萄糖部分聚合形成水溶性和水不溶性葡聚糖。虽然在变形链球菌和唾液链球菌菌株中已鉴定出多个gtf基因，但在戈登氏链球菌Challis菌株中，单个基因（命名为gtfG）编码其GTF。gtfG在已鉴定的gtf中也很独特，因为它有一个描述的调控决定簇rgg。此外，戈登氏链球菌中的GTF活性在高水平和低水平之间经历可逆的相变。为了深入了解这个新型GTF系统，测定了gtfG的核苷酸序列，发现它由一个4734个碱基对的开放阅读框组成，编码一种推导分子量约为174,000的蛋白质。gtfG与其他已测序的gtf相似，有一个保守的信号序列，接着是一个gtfG特有的约600碱基对区域、一个编码假定催化活性位点的保守区域以及羧基末端区域中与葡聚糖结合有关的一系列六个直接重复序列。虽然将gtfG与其他gtf进行比较没有显示出编码酶不依赖引物的基础或葡聚糖产物的性质，但gtfG序列数据为进一步研究这些酶提供了重要依据。
