Detection of the single-stranded DNA of Streptomyces plasmid pSA1.1 and a binding histone-like protein

Expression analysis of the spi gene in the pock-forming plasmid pSA1.1 from Streptomyces azureus and localization of its product during differentiation

The sporulation inhibitory gene spi in the pock-forming conjugative plasmid pSA1.1 of Streptomyces azureus was introduced into cells via a high or low copy number vector to examine the effect of gene dosage on the growth of Streptomyces lividans TK24 as a host. In transformants carrying a high spi copy number, nutrient mycelial growth was inhibited, as was morphological differentiation from substrate mycelium to aerial mycelium on solid media. The degree of inhibition depended on the spi gene dosage, but the presence of pSA1.1 imp genes, which encode negative repressor proteins for spi, relieved the inhibition. Confocal images of Spi tagged with enhanced green fluorescent protein in cells on solid media revealed that spi expression was initiated at the time of elongation of substrate mycelium, that its expression increased dramatically at septation in aerial hyphae, and that the expression was maximal during prespore formation. Expression of spi covered the whole of the hyphae, and the level of expression at the tip of the hyphae during prespore formation was about sixfold greater than during substrate mycelial growth and threefold greater than during aerial mycelial growth. Thus, localized expression of spi at particular times may inhibit sporulation until triggering imp expression to repress its inhibitory effects.

Disruption of the hup gene encoding a histone-like protein HS1 and detection of HS12 of Streptomyces lividans

When the latter half of the hup gene encoding a histone-like protein HS1 of Streptomyces lividans TK24 was replaced by the kanamycin resistance gene, the hup mutant EY1 grew slowly in liquid medium and this delay was overcome by introduction of the complete hup. EY1 sporulated normally on solid medium, with no serious defects as observed in hupAB mutants of Escherichia coli. Therefore, HS1 probably has a role in growth in the presence of liquid medium and this organism may possess another histone-like protein with functions overlapping those of HS1. We cloned the hup2 gene encoding another histone-like protein HS12, which has two motifs of prokaryotic histone-like protein and eukaryotic histone H1. The amount of HS12 increased in EY1, determined by western blotting analysis using an anti-His-tagged HS12 polyclonal antibody. We are entertaining the notion that the increased amount of HS12 partially suppressed the defects caused by the hup mutation.

Gene encoding a replication initiator protein and replication origin of conjugative plasmid pSA1.1 of Streptomyces cyaneus ATCC 14921

pSA1.1 is a 9.1-kb multicopy plasmid originally isolated from Streptomyces cyaneus (formerly S. azureus) ATCC 14921. This plasmid accumulates single-stranded DNA in S. lividans and is therefore considered to replicate by a rolling-circle replication. In the present work, the rep gene encoding the replication initiator protein and the replication origin ori of pSA1.1 were determined. The rep and ori are located on separate regions. The Rep protein of pSA1.1 belongs to superfamily I which includes A proteins of phages. Nucleotide sequence of the surrounding putative nicking site of pSA1.1 shows good agreement with those of the pC194 group plasmids and phages. The direction of replication was also determined.

Cloning and sequencing of the hup gene encoding the histone-like protein HSl of Streptomyces lividans

The hup gene encoding the histone-like HU-type protein HSl of Streptomyces lividans TK24 was cloned and sequenced. The deduced N-terminal amino acid sequence, molecular mass (9851 Da) and pI (9.95) are in good agreement with characteristics of the HSI protein. The hup transcript of about 500 nucleotides was detected. The 2.3-kb HincII fragment containing the hup gene hybridized with the AseI fragment C in the 9-10 o'clock region of the chromosome of S. lividans ZX7.