Many strains of the phytopathogen Pseudomonas syringae contain mutually compatible plasmids that share extensive regions of sequence homology and essential replication determinants. The replication regions of two compatible large plasmids involved in virulence or pathogenicity, pPT23A from P. syringae pv. tomato strain PT23 and pAV505 from P. syringae pv. phaseolicola strain HR11302A, were isolated. DNA sequencing of the origins of replication revealed homologous ORFs, designated ORF-Pto and ORF-Pph, respectively. Both ORFs are 1311 bp long and encode peptides of 437 amino acids with predicted molecular masses of 48259 (Pto) and 48334 (Pph) Da. Expression of the two ORFs in Escherichia coli produced peptides of 50 kDa (Pto) and 56 kDa (Pph). The predicted peptides showed an overall identity of 897 %, being highly conserved from residues 1 to 373, but showing considerable variation in their C-terminal regions (50% identity over the last 64 aa). The two ORFs had significant similarity with the putative replication protein from plasmid pTiKl2 of Thiobacillus intermedius and other ColE2-related plasmids. However, both peptides were 100 residues longer than any of the known ColE2-related rep sequences. Subcloning of fragments from the replication region of pPT23A revealed the presence of a t least three incompatibility determinants, designated IncA, lncB and IncC. Partial sequencing of the region downstream of ORF-Pto revealed homology to the rulAB genes, involved in UV resistance, from plasmid pPSR1. It is proposed that the replication origin of pPT23A serves as the prototype of a family of related plasmids.

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The rodent genus Peromyscus is the most numerous and species rich mammalian group in North America. The naturally occurring diversity within this genus allows opportunities to investigate the genetic basis of adaptation, monogamy, behavioral and physiological phenotypes, growth control, genomic imprinting, and disease processes. Increased genomic resources including a high quality genetic map are needed to capitalize on these opportunities. We produced interspecific hybrids between the prairie deer mouse (Peromyscus maniculatus bairdii) and the oldfield mouse (Peromyscus polionotus) and scored meiotic recombination events in backcross progeny. A genetic map was contructed by genotyping of backcross progeny at 185 gene-based and 155 microsatellite markers representing all autosomes and the X chromosome. Comparison of the constructed genetic map with the molecular maps of Mus and Rattus and consideration of previous results from interspecific reciprocal whole chromosome painting allowed most linkage groups to be unambiguously assigned to specific Peromyscus chromosomes. Based on genomic comparisons, this Peromyscus genetic map covers approximately 83% of the Rattus genome and 79% of the Mus genome. This map supports previous results that the Peromyscus genome is more similar to Rattus than Mus. For example, coverage of the 20 Rattus autosomes and the X chromosome is accomplished with only 28 segments of the Peromyscus map, but coverage of the 19 Mus autosomes and the X chromosome requires 40 chromosomal segments of the Peromyscus map. Furthermore, a single Peromyscus linkage group corresponds to about 91% of the rat and only 76% of the mouse X chromosomes.

We describe 9-year-old twin girls who were thought to be monozygotic but who differed greatly in physical appearance and growth pattern. One twin had Ullrich-Turner syndrome (UTS), 45,X/46,XX mosaicism in peripheral blood, and only 45,X cells in skin fibroblasts. The phenotypically normal twin also had 45,X/46,XX mosaicism in blood but only 46,XX cells in cultured fibroblasts. Analysis of DNA marker patterns in blood lymphocytes and in skin fibroblasts confirmed monozygosity with a probability of 99.97%. This case is compared with other reported cases of discordance for UTS in twins. It is concluded that essentially all of the differences between the two twins can be explained by loss of an X chromosome early in embryogenesis with complete separation of 45,X and 46,XX cell lineages at the time of the twinning event. The presence of mosaicism in the peripheral blood of both twins is presumably due to anastomoses between the placentae resulting in a mixture of the two cell populations in the hematopoietic tissue.