[Structural peculiarities of the SCP2 plasmid of Streptomyces coelicolor A3(2)]. / Strukturnye osobennosti plazmidy SCP2 Streptomyces coelicolor A3(2).

Structural peculiarities of SCP2 plasmid isolated from different derivatives of Streptomyces coelicolor A3(2) were studied. By means of heteroduplexing 800 b.p. DNA insertion in SCP2 plasmid of S18-1 derivative was detected. The position of this insertion was localised on the SCP2 restriction map. A transposon-like structure with similar characteristics was detected and localised in different variants of SCP2 plasmid. This 600 bp DNA region is flanked by 20 bp inverted repeats and has the single EcoRI cleavage site. It is noted that the stretching of single-strand DNA circles of SCP2 plasmid was significantly less than that of single-strand DNA circles of pBR322 and PAS3; Tn9 plasmids. This may likely depend on the GC content of different plasmids.

[Genetic instability of the production of antibiotic substances controlled by the SCP2 plasmid of Streptomyces coelicolor A3(2)]. / Geneticheskaia nestabil'nost' produktsii antibioticheskikh veshchestv, kontroliruemoi SCP2-plazmidoi Streptomyces coelicolor A3(2).

Streptomyces coelicolor A3(2) strain bearing a variant of SCP2 plasmid produces three antibiotic substances: amromycin and streptocins A and B. After growth at elevated temperature (37 degrees C) of S. coelicolor A3(2), mutants which are not capable of producing amromycin and streptocins A and B (ant- mutants) were formed at high frequency (50%). These mutants retained SCP2 plasmid. Genetic analysis demonstrates that Ant phenotype is caused by a mutation in SCP2 plasmid. Genetic analysis demonstrates that Ant phenotype is caused by a mutation in SCP2. Heteroduplex and electrophoretic analysis of SCP2 DNAs from mutant variants indicates that these plasmids contained the identical deletion of 800 +/- 100 base pairs, as compared to SCP2 DNA of the initial strain. Ant variants revert to the initial phenotype at a frequency of 1.10(-2) to 1.10(-3). In turn, revertants from Ant variants a high frequency, similar to the initial strain. It is suggested that reversible Ant+ in equilibrium or formed from Ant- transitions might be the result of transposition of a genetic element in SCP2 controlling production of amromycin and streptocins A and B.

[Physical mapping of Streptomyces coelicolor A3(2). V. Structural modifications of actinophage phiC43 DNA molecules]. / Fizicheskoe kartirovanie aktinofagov Streptomyces coelicolor A3(2). V. Strukturnye modifikatsii molekul DNK aktinofaga phiC43.

As shown by genetical and physical methods, the total preparation of phiC43 phage obtained after spontaneous induction of the prophage from S. lividans 803 strain is a heterogenous population. The wild-type phage (phi C43 wt) is only represented in 5--10% of the population. The majority of phage variants are not able to establish the lysogenic state. The structure of DNA molecules of some phages from the total preparations was characterized by electron microscopy of DNA heteroduplexes. Molecules of phiC43 wt DNA appeared to be completely homologous to those of recently studied phiC62 phage, except for two small regions of approximately 0.3 kb in the central part. Phage variants defective in establishment of the lysogenic state were distributed to two groups. One of them consists of deletion variants, the other--deletion/insertion variants. Deletions in DNA molecule of all nonlysogenizing phage overlap. The region of overlapping seems to be responsible for establishment of the lysogenic state. In the same region, deletion of DNA molecules of mutant phiC311 yg2 has been located. Three deletion/insertion variants contain homologous foreign sequences of various length. It is likely that these insertions are fragments of the host chromosomal DNA.

[Physical mapping of Streptomyces coelicolor A3(2) actinophage DNA. II. Transposon-like structure in DNA molecules of phiC43 phage DNA, localization of region responsible for establishment of the lysogenic state]. / Fizicheskoe kartirovanie DNK aktinofagov Streptomyces coelicolor A3(2). II. Transpozonopodobnaia struktura v molekuliakh DNK faga phiC43, lokalizatsiia oblasti, otvetstvennoi za ustanovlenie lizogennogo sostoianiia.

Structural properties of DNA molecules of phages phi C43, phi C43del and mutant phage phi C311yg33 were studied. Actinophages phi C43del and phi C311yg33 have been isolated and shown to have a phenotype characteristic of phages defective in integration, i. e. turbid plaques and inability to establish the lysogenic state. By means of heteroduplexing, deletions were mapped in the genomes of these phages. DNA molecules of phi C43del and phi C11yg33 are devoid of the common fragment, which suggests that the mutant phenotypic character is associated with structural alterations in DNA molecules. The presence of transposon-like structure in phi C43 DNA molecules has been inferred from the analysis of phi C43/phi C43del heteroduplexes and phi C43 homoduplexes. Also, a deletion in phi C43 genome has been detected covering the same region where deletions in phi C43del and phi C11yg33 DNAs were located.