single strand DNA while RecG shows a 3Ј to 5Ј DNA Department of Molecular Microbiology, Research Institute for helicase activity (Tsaneva et al., 1993; Whitby et al., Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, 1994). Osaka 565, Japan In the RuvABC pathway, RuvC is a specific endonucle-1 Corresponding author ase that resolves Holliday junctions (Dunderdale et al., 1991;Iwasaki et al., 1991). RecG, which functions in The RecG protein of Escherichia coli is a DNA helicase the alternative pathway, has been suggested to promote that promotes branch migration of the Holliday juncjunction resolution by driving branch migration in the tions. We found that overproduction of RecG protein opposite direction from that promoted by RecA protein drastically decreased copy numbers of ColE1-type (Whitby et al., 1993;Whitby and Lloyd, 1995). These plasmids, which require R-loop formation between the authors proposed that RecG plays a role in preventing template DNA and a primer RNA transcript (RNA unproductive recombination by reversing the invasion of II) for the initiation of replication. RecG efficiently a 5Ј single-stranded DNA end into the homologous duplex inhibited in vitro ColE1 DNA synthesis in a reconstitu- . ted system containing RNA polymerase, RNase HI andThe recG and ruv genes play different roles in alternative DNA polymerase I. RecG promoted dissociation of mechanisms of stable DNA replication (SDR), which do RNA II from the R-loop in a manner that required not require the chromosomal replication origin (oriC), ATP hydrolysis. These results suggest that overDnaA initiator protein or concomitant protein synthesis produced RecG inhibits the initiation of replication (Asai and Kogoma, 1994a). Mutations in the ruv or recG by prematurely resolving the R-loops formed at the gene stimulate inducible SDR (iSDR), which is a part of replication origin region of these plasmids with its SOS responses, suggesting that this mode of SDR involves unique helicase activity. The possibility that RecG D-loops or Holliday junctions made by RecA (Asai and regulates the initiation of a unique mode of DNA Kogoma, 1994b). recG mutants, but not ruv mutants, replication, oriC-independent constitutive stable DNA stimulate constitutive SDR (cSDR), which was found replication, by its activity in resolving R-loops is disoriginally in RNase HI-defective (rnhA) mutants, and recG cussed.rnhA double mutants are inviable. These results suggested

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Background: All the ruvA, ruvB and ruvC mutants of Escherichia coli are sensitive to treatments that damage DNA, and are mildly defective in homologous recombination. It has been reported that the ruv mutants form nonseptate, multinuclear filaments after low doses of UV irradiation, dependent on the sfiA gene product. In vitro, the RuvAB complex promotes the branch migration of Holliday junctions, and RuvC resolves the junctions endonucleolytically.

The products of the recG and ruvAB genes of Escherichia coli are both thought to promote branch migration of Holliday recombination intermediates by their junction specific helicase activities in homologous recombination and recombination repair. To investigate the in vivo role of the recG gene, we examined the effects of a recG null mutation on cell division and chromosome partition. After UV irradiation at a low dose (5J/ m 2 ), ∆recG mutant formed filamentous cells with unpartitioned chromosomes. A mutation in the sfiA gene, which encodes an SOS-inducible inhibitor of septum formation, partially suppressed filamentation of recG mutant cells, but did not prevent the formation of anucleate cells. The sensitivity to UV light and the cytological phenotypes after UV irradiation of a recA recG double mutant were similar to a recA single mutant, consistent with the role of recG, which is assigned to a later stage in recombination repair than recA. The recG ruvAB and recG ruvC double mutants were more sensitive to UV, almost as sensitive as the recA mutant and showed more extreme phenotypes concerning filamentation and chromosome nondisjunction, both after UV irradiation and without UV irradiation than either recG or ruv single mutants. The recG polA12 (Ts) mutant, which is temperature sensitive in growth, formed filamentous cells with centrally located chromosome aggregates when grown at nonpermissive temperature similar to the UV irradiated recG mutant. These results support the notion that RecG is involved in processing Holliday intermediates in recombination repair in vivo. We suggest that the defect in the processing in the recG mutant results in accumulation of nonpartitioned chromosomes, which are linked by Holliday junctions.

Human RSV causes an annual epidemic of respiratory tract illness in infants and in elderly. Mechanisms by which RSV antagonizes IFN-mediated antiviral responses include inhibition of type I IFN mRNA transcription and blocking signal transduction of JAK/STAT family members. The suppressor of cytokines signaling (SOCS) gene family utilizes a feedback loop to inhibit cytokine responses and block the activation of the JAK/STAT signaling pathway. To evaluate the potential of SOCS molecules to subvert the innate immune response to RSV infection, eight SOCS family genes were examined. RSV infection up-regulated SOCS1, SOCS3, and CIS mRNA expression in HEp-2 cells. Suppression of SOCS1, SOCS3 and CIS by short interfering ribonucleic acid (siRNA) inhibited viral replication. Furthermore, inhibition of SOCS1, SOCS3, or CIS activated type I IFN signaling by inducing STAT1/2 phosphorylation. These results suggest that RSV infection escapes the innate antiviral response by inducing SOCS1, SOCS3 or CIS expression in epithelial cells.