The structures of a number of enzymes involved in polynucleotide transfer have been observed to have the same basic fold as ribonu-clease H (RNaseH; Katayanagi et al., 1990, 1992; Yang et al., 1990). Members of this family include RNase H, retroviral integrase, Holiday junction RuvC resolvase, TN5 transposase, the RNase H domain of retroviral reverse transcriptase, a core fragment of bacteriaphage Mu transposase, and the 3'-5' exonuclease domains from several DNA polymerase structures, including the Klenow fragment (Ollis et al., 1985; Davies et al., 1991, 2000; Ariyoshi et al., 1994; Dyda et al., 1994; Rice and Mizuuchi, 1995). The sequence identity among family members is generally <15%. At the center of the structure is a five-stranded P-sheet, aligned with a strand order of 3-2-1-4-5. The second strand is antiparallel to the other four strands (Fig. 17.1.31). The number and location of the helices are less conserved than the central P-sheet. Helices A and E are topologically more conserved than the other helices. They are located between strands 3 and 4, and at the C-terminal of strand 5 in sequence, primarily interacting with the central P-sheet. The number of helices between strands 4 and 5 varies, as do the helices after helix E (Fig. 17.1.31). The family can be further divided into RNase- (e.g., HIV-1 reverse transcriptase RNase H, E. coli RNase H, Archeon Class II RNase H) and integrase-like structures (e.g., integrase, Mu A transposase, RuvC) with greater structure resemblance observed between the members of each subclass. Limited structural homology, particularly among the central five-stranded P-sheet, is also observed with Mut S domain II, actin-like ATPase domains, and ribosomal proteins L18 and S11.
Was this article helpful?
Parenting is a challenging task. As a single parent, how can you juggle work, parenting, and possibly college studies single handedly and still manage to be an ideal parent for your child? Read the 65-page eBook Single Parenting Becoming The Best Parent For Your Child to find out how. Loaded with tips, it can inspire, empower, and instruct you to successfully face the challenges of parenthood.