Genomic relatedness ofStaphylococcus aureusphages of the International Typing Set and detection of serogroup A, B, and F prophages in lysogenic strains

On the basis of HindIII-restriction digest analysis of genomic DNAs, the S. aureus bacteriophages of the International Typing Set were divided into five clusters designated as A, F, Ba, Bb, and Bc. The clusters A and F include all the phages of serogroups A and F and correspond to species 3A and 77 proposed by Ackermann and DuBow (1987). On the other hand, the phages of serogroup B were divided into three clusters designated as Ba, Bb, and Bc that differ significantly each from the other in their restriction patterns. The clusters Ba and Bb may represent two separate species, while the cluster Bc may include more than one phage species. For each of the phage serogroups A, B, and F, common HindIII-restriction fragments of phage 3A (1700 bp), of 53 (4060 bp), and of 77 (8300 bp) were used for the preparation of probes specific to the phages of serogroups A, B, and F. These probes were very effective, making it possible to detect up to three different prophages in a given lysogenic strain at the same time. Restriction enzyme maps of phages 3A, 53, and 77, each representing a different serogroup, were constructed. The restriction maps of phage 3A and that of phage 77 are linear, whereas that of phage 53 is circular and exhibits a circular permutation. DNAs of the phages of serogroups A and F have cohesive ends. On each restriction map, the sites corresponding to specific probes are indicated. The size of intact genomic DNA of all phages estimated by PFGE varies within the range of 41.5-46.2 kb.Key words: Staphylococcus aureus, bacteriophages, prophage specific probes, restriction endonuclease maps.

Clarification of the structure of the ampicillin-resistance plasmid RSF0885 from Haemophilus influenzae HR-885 serotype b

The nonconjugative ampicillin-resistance plasmid RSF0885 has been reported to be as small as 2.9 MDa and as large as 4.1 MDa with at least two restriction enzyme maps reported. In addition, the source of the original plasmid has been reported to be Haemophilus influenzae and Haemophilus parainfluenzae. Characterization of the source strains and sequencing data of the plasmids revealed that H. influenzae serotype b was the original source strain and that ISI-K in the larger plasmid was presumably acquired when the smaller plasmid was maintained in Escherichia coli in S. Falkow's laboratory during the late 1970s.Key words: Haemophilus influenzae, Haemophilus parainfluenzae, RSF0885, ampicillin resistance, ISI-K

Molecular analysis of the Coprinus cinereus mating type A factor demonstrates an unexpectedly complex structure.

We report here the molecular cloning of the A43 mating type factor from Coprinus cinereus, a basidiomycetous fungus. Our molecular analyses revealed an unexpected source of variation in the A factor. Though genetic studies have demonstrated that A has two subunits, alpha and beta, we located three nonoverlapping fragments in the A43 region that have A factor function following DNA-mediated transformation. The three fragments demonstrate no similarity to one another as judged by restriction enzyme maps and by hybridization on Southern blots. We conclude that the A43 factor is composed of at least three subunits. When strains carrying different A factors are examined by hybridization to the cloned subunits, extensive polymorphism is seen. Both intensity of hybridization and restriction fragment lengths vary between strains. Some strains fail to show any hybridization to a probe. In contrast, other strains from widely separated geographic locations apparently share very similar subunits. From comparative restriction enzyme mapping of A43 and a mutated A43 factor, we inferred that a 12-kb deletion in the A factor was responsible for the constitutive, dominant phenotype of the mutated A factor. The results of transformation experiments support an activator model for the activity of the A factor in regulating the A pathway.

Variation of the intergenic spacer region of ribosomal DNA in cultivated and wild rice species

Spacer-length variation in ribosomal DNA (rDNA) was surveyed in two cultivated rice species and their wild relatives. Among 243 accessions observed, 18 different spacer-length variants were detected. Length heterogeneity was found within and among species as well as within individuals. Conventional genetic analysis revealed that two spacer-length variants were located at two unlinked loci. Restriction enzyme maps showed that length heterogeneity resulted from repetition of short repeated sequences in the intergenic spacer region in the Asian cultivar and its progenitor; however, the spacer region greatly differed from those of reproductively isolated taxa with respect to the length and the sequence. Furthermore, the Asian cultivated species and its progenitor were highly polymorphic for rDNA spacer-length variation and they were differentiated in frequencies of spacer-length variants as well as varietal groups within the cultivated species. Asian cultivars tended to carry homogeneous repeats of rDNA compared with their progenitor, suggesting different forms of homogenization occurring in Asian cultivars.Key words: ribosomal DNA, intergenic spacer, polymorphism, inheritance, Oryza.

Structure of the c-Ki-ras gene in a rat fibrosarcoma induced by 1,8-dinitropyrene.

Restriction enzyme maps were made of the region around exons 1 and 2 of activated c-Ki-ras of a fibrosarcoma (1,8-DNP2) induced in a rat by 1,8-dinitropyrene. Nucleotide sequence analysis revealed that activated c-Ki-ras shows a G----T transversion in codon 12 and consequently encodes cysteine instead of glycine in normal rat c-Ki-ras.