Koonin E V, Rudd K E
National Center for Biotechnology Information, National Library of Medicine, NIH, Bethesda, Maryland 20894, USA.
Protein Sci. 1996 Jan;5(1):178-80. doi: 10.1002/pro.5560050124.
DNA and RNA helicases of superfamily I are characterized by seven conserved motifs. The five N-terminal motifs are separated from the two C-terminal ones by a spacer that is highly variable in both sequence and length, suggesting the existence of two distinct domains. Using computer methods for protein sequence analysis, we show that PhoH, an ATP-binding protein that is conserved in Escherichia coli and Mycobacterium leprae, is homologous to the putative N-terminal domain of the helicases, whereas the putative E. coli protein YjhR is homologous to the C-terminal domain. These findings suggest that the N-and C-terminal domains of superfamily I helicases have distinct activities, with only the N-terminal domain having the ATPase activity. It is speculated that PhoH and YjhR have evolved from helicases through deletion of the portions of the helicase genes coding for the C- and N-terminal domain, respectively.
超家族I的DNA和RNA解旋酶具有七个保守基序。五个N端基序与两个C端基序被一个间隔区分开，该间隔在序列和长度上高度可变，这表明存在两个不同的结构域。通过计算机蛋白质序列分析方法，我们发现PhoH是一种在大肠杆菌和麻风分枝杆菌中保守的ATP结合蛋白，它与解旋酶假定的N端结构域同源，而假定的大肠杆菌蛋白YjhR与C端结构域同源。这些发现表明，超家族I解旋酶的N端和C端结构域具有不同的活性，只有N端结构域具有ATP酶活性。据推测，PhoH和YjhR分别通过缺失解旋酶基因中编码C端和N端结构域的部分而从解旋酶进化而来。
