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The herpes simplex virus type 1 (HSV‐1) transcripts that can be detected during latent infection by Northern blot analysis in human and experimental animal sensory ganglia are encoded by diploid genes. To investigate their role in latent infection we studied HSV‐1 variant 1704, which has deleted most of the IRL copy of the coding region of these RNAs and has a 1.2‐kb deletion that is immediately upstream of the coding region of the TRL copy. During primary infection, 1704 replicated in trigeminal ganglia with kinetics similar to the parent virus (17+) and established latent infection. However, while explant reactivation of latent HSV‐1 from trigeminal ganglia was detected in 100% of 17+ infected mice within 7 days, the reactivation of 1704 was significantly delayed, and 31 days elapsed before eight out of nine mice became virus positive. The recognized HSV‐1 latency‐associated RNAs were not detected during the latent state of 1704 by Northern blot analysis or in situ hybridization, which implies that the 1.2‐kb deletion may contain the promoter or other important regulatory elements. The data indicate that detectable levels of these latency‐associated transcripts are not required for viral replication, establishment, or maintenance (greater than 6 weeks) of HSV‐1 latency in trigeminal ganglia, but suggest a role in reactivation.

Pseudomonas aeruginosa is an obligate aerobe that is virtually ubiquitous in the environment. During aerobic respiration, the metabolism of dioxygen can lead to the production of reactive oxygen intermediates, one of which includes hydrogen peroxide. To counteract the potentially toxic effects of this compound, P. aeruginosa possesses two heme-containing catalases which detoxify hydrogen peroxide. In this study, we have cloned katB, encoding one catalase gene of P. aeruginosa. The gene was cloned on a 5.4-kb EcoRI fragment and is composed of 1,539 bp, encoding 513 amino acids. The amino acid sequence of the P. aeruginosa katB was ϳ65% identical to that of a catalase from a related species, Pseudomonas syringae. The katB gene was mapped to the 71-to 75-min region of the P. aeruginosa chromosome, the identical region which harbors both sodA and sodB genes encoding both manganese and iron superoxide dismutases. When cloned into a catalase-deficient mutant of Escherichia coli (UM255), the recombinant P. aeruginosa KatB was expressed (229 U/mg) and afforded this strain resistance to hydrogen peroxide nearly equivalent to that of the wild-type E. coli strain (HB101). The KatB protein was purified to homogeneity and determined to be a tetramer of ϳ228 kDa, which was in good agreement with the predicted protein size derived from the translated katB gene. Interestingly, KatB was not produced during the normal P. aeruginosa growth cycle, and catalase activity was greater in nonmucoid than in mucoid, alginate-producing organisms. When exposed to hydrogen peroxide and, to a greater extent, paraquat, total catalase activity was elevated 7-to 16-fold, respectively. In addition, an increase in KatB activity caused a marked increase in resistance to hydrogen peroxide. KatB was localized to the cytoplasm, while KatA, the ''housekeeping'' enzyme, was detected in both cytoplasmic and periplasmic extracts. A P. aeruginosa katB mutant demonstrated 50% greater sensitivity to hydrogen peroxide than wild-type bacteria, suggesting that KatB is essential for optimal resistance of P. aeruginosa to exogenous hydrogen peroxide.