Attachment of the chromosomal terminus of Bacillus subtilis to a fast-sedimenting particle

After gently lysed protoplasts of exponential phase cells of Bacillus subtilis were treated with restriction endonuclease BamHI, 99% of the DNA did not sediment with the plasma membrane. This DNA was fractionated on sucrose gradients into (i) a fast-sedimenting fraction highly enriched for genes from the origin and terminus (purA and ilvA), (ii) a 50 to 100S component also enriched for purA and ilvA, and (iii) the bulk of the DNA. The fast-sedimenting fraction was dissociated by Sarkosyl; this fraction contained a substantial amount of protein and is probably a membrane subparticle. The S value of the 50 to 100S component was not greatly affected by Sarkosyl treatment, but these particles were unable to penetrate an agarose gel during electrophoresis and were retained by nitrocellulose filters. The terminus DNA in the fast-sedimenting fraction and the 50 to 100S component contained a large restriction fragment (1.5 x 10(7) to 2.0 x 10(7) daltons) encoding ilvA, thyB, and ilvD. The bulk of the SP beta prophage and metB, which lie to the right and left, respectively, of the ilvA-ilvD cluster, were not part of the complex. citK, which lies to the right of SP beta, appeared to be present in the fast-sedimenting complexes. The neighboring genes kauA and gltA were not part of the fast-sedimenting complexes. The presence of terminus DNA in the fast-sedimenting components was also demonstrated by a radiochemical method.     

Net genetic and temporary epistatic or maternal environmental responses to selection for egg production in chickens

The difference between progeny from selected and unselected parents (T) was experimentally partitioned into net genetic change (G_A), temporary favorable epistatic combinations (G_EP) and egg-transmitted maternal environment (M) in two strains of Leghorns selected over 14 years for early pure-strain egg production. Differences among progeny from selected sires and dams, selected sires only, selected dams only, unselected sires and dams and the parental generation were equated to expected G_A, G_EP and M responses for each trait. Total response was 3.3% for early egg number, 3.7% for total egg number, 0.5% for egg weight, 3.8% for early egg mass and 4.2% for total egg mass. Among progeny that survived the test period and were judged to be normal, total response was 2.6% for total number of eggs, 3.0% for early egg mass and 3.1% for total egg mass. The percentage of T attributed to G_A was 9% for early egg number, 24% for total egg number, 43% for early egg mass and 47% for total egg mass; but 52% for total egg number, 98% for early egg mass and 71% for total egg mass of normal survivors. Temporary maternal selection responses (M) were (1) positive for number of eggs and egg masses, (2) greater for all progeny than for normal survivors, and (3) increased with progeny age. The results suggest that M was caused by reduced egg-transmitted disease. Epistatic selection response was positive for earlier sexual maturity and for number of eggs, but negative for egg weight and thus was small for egg masses. Temporary epistatic and maternal responses can explain overestimation of additive genetic response from offspring-parent regression or from replicated single-generation selection and apparent superiority of mass selection over family or combined selection.     

Corneal endothelium: a modified method for cultivation

A modified method for establishing cultures of rabbit corneal cells is described. The new technique utilized a Lucite disc in combination with a Tygon ring for growth of pure cell cultures and was compared with an explant method for growing cells. Each method provided adequate cell cultures for biochemical or ultrastructure studies of rabbit corneal cells, but the ring and disc method described here allowed the isolation of specific cell types without the interference of stromal cell contamination.     

Isolation and characterisation of deletion mutants involving the transfer genes of P-group plasmids in Pseudomonas aeruginosa

Summary The P-group plasmids RP1 and R26 are recovered at low frequency following conjugal transfer to B3-lysogens of P. aeruginosa PAO. The rare carbenicillin-resistant transcipients that do arise are usually transfer-defective (Tra^-) and may show the loss of other plasmid borne functions, namely kanamycin-resistance (Km^r) and reduced plating of phage GlOl (Spp⁺). The four phenotypic classes that occur among the Tra^- derivatives are respectively, Tra^- (69–81%), Tra^- Spp^- (12–30%), Tra^- Km^s and Tra^- Km^s Spp^- (0.2–1%), of which the latter three are due to plasmid deletions. This is seen from the sizes of the plasmids carried by these bacteria and from the transductional analysis of the R26-derivatives. Thus, although R26 (MW=52×10⁶ daltons) is too large to be transduced by phage F116L (MW=40×10⁶), this is possible for its Tra^- Km^s and Tra^- Km^s Spp^- derivatives. The phenotypes and frequencies of the various transcipient classes suggests that the gene order Km..Tra..Spp occurs in both RP1 and R26, and that Spp is more closely linked to Tra than is Km. These conclusions are supported by the sizes of the plasmid mutants since deletions spanning the loci Km Tra Spp, Km Tra, and Tra Spp involve the loss of DNA of MW 8-17×10⁶, 5-13×10⁶ and 1-9×10⁶ daltons respectively.Whilst all the transcipients displayed the incompatibility properties of the parent plasmids (Inc⁺), only some retained plasmid surface exclusion (Sfx⁺). Moreover, a strict correlation existed between the Sfx and Spp phenotypes such that the transcipients were either wild type, Sfx^- Spp^-, or displayed an intermediate phenotype for both characters. This suggests that these phenotypes are controlled by closely linked genes or are different manifestations of the same gene function. The deletion map of these various markers in both RP1 and R26 therefore seems to be Km..Tra..Sfx/Spp..Inc.