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We have compared the adenosine triphosphatase (ATPase) activity of mitochondria prepared from wild-type Neurospora crassa and from poky, a maternally inherited mutant known to possess defective mitochondrial ribosomes and reduced amounts of cytochromes aa3 and b. poky contains two distinct forms of mitochondrial ATPase. The first is normal in its Km for ATP, specificity for nucleotides and divalent cations, pH optimum, cold stability, and sensitivity to inhibitors (oligomycin, N,N-dicyclohexyl carbodiimide, and adenylyl imidodiphosphate). The fact that membrane-bound, cold-stable, oligomycin-sensitive ATPase activity is present in poky (with an activity of 1.93 +/- 0.03 mumol/min-mg of protein compared with 1.33 +/- 0.07 mumol/min-mg of protein in the wild-type strain) and also in chloramphenicol-grown wild-type cells suggests that products of mitochondrial protein synthesis play only a limited role in the attachment of the mitochondrial ATPase to the membrane in Neurospora. poky also contains a second form of mitochondrial ATPase, which has an activity of 1.5 +/- 0.2 mumol/min-mg of protein, is oligomycin sensitive but cold labile, and presumably is attached less firmly to the mitochondrial membrane. The two forms, added together, represent a substantial overproduction of mitochondrial ATPase by poky.

Genetic and segregation analysis of Escherichia coli strains containing a partial duplication of the trp operon reveal that the 2.5-min-long region trpD-purB is duplicated in tandem in the chromosome. The adjacent loci cysB and fabD are not duplicated. Although one copy of the duplicated region is longer than the maximum size of bacteriophage P1kc transducing fragments, the frequency at which the duplicated segment trpDCBA is transferred by transduction to tonB-trp deletion strains is equal to that observed for transfer of the normal trp operon. This suggests that three-point recombination events believed to account for transduction of long duplications occur as frequently as two-point recombination events believed to account for normal transduction. Cotransduction frequencies of trpDCBA with the duplicated loci tonB, galU, tyrT, and hemA are very similar to those for the trp operon with the same loci. This indicates that normal genetic linkage is maintained during the three-point recombination event. However, purB, which is normally unlinked to trp by transduction, is closely linked to trpDCBA and thus must be near the repeat point of the duplication. Transduction tests with point mutations in the trp operon indicated that the repeat point occurs near the normal boundary between trpE and trpD. Segregation analysis of heterogenotes constructed from tonB-trp deletion strains shows that the frequency at which a marker is lost is approximately proportional to its distance from the repeat point. This finding is consistent with a random, singlesite crossover event during segregation. Several observations indicate that non-reciprocal genetic exchange also occurs between copies of the duplication. Analysis of heterogenotes containing dadR1 and dadR(+) demonstrate that the mutant allele is transdominant.

We have described here two distinct types of carrier-specific helper T cells which act independently and synergistically to augment the B-cell response to a hapten. They are separable by passage through a nylon wool column. The first type of helper T cell, which we designate as Th1, is nylon nonadherent, and can help the response of hapten-primed B cells only if the haptenic and carrier determinants are present on a single molecule (cognate interaction). The second type of helper T cell, Th2, adheres to the nylon wool column, and can help the B-cell response to a hapten coupled to a heterologous carrier upon stimulation with unconjugated relevant carrier (polyclonal interaction). The addition of a small number of Th2 to the mixture of Th1 and B cells significantly augmented the net response to the hapten carrier conjugate. Both Th1 and Th2 cells belong to the Lyt-1+,2-,3- subclass. Th1 has no detectable Ia antigen, whereas Th2 is killed by certain anti-Ia antisera and complement. The Ia antigen detected on Th2 was found to be controlled by a locus in the I-J subregion. The results clearly established the fact that there are two distinct pathways in the T- and B-cell collaboration, which involves two different subsets of carrier-specific helper T cells.

Modification of 5--6 arginine residues of thrombin with 1,2-cyclohexanedione has resulted in the selective abolition of the heparin sensitivity of the enzyme's reaction with antithrombin-III, whereas the antithrombin-III sensitivity of native and modified thrombin was indistinguishable. It is suggested that heparin accelerates the thrombin antithrombin-III reaction by interacting with thrombin.