Lipolysis induction in adipocytes by a protein from tumor cells

Extracts of thymic lymphoma that are obtained from AKR mice and are kept in the cold for at least several days can induce lipolytic activity in rat adipocyte suspensions. Freshly prepared extracts have low activity but contain a low molecular weight material of less than 10,000 daltons that aggregates on standing in the cold and becomes active. Treatment of aged extracts with trypsin causes a loss in activity indicating that the active material is a protein. It has been obtained in partially purified form, is relatively heat stable, and is not a lipase. Activity was also demonstrated in AKRXDBA/2 lymphoma (induced by AKR SL3-3 virus) and in transplanted lymphomas from a Friend-virus-induced erythroleukemia cell line in DBA/2 mice, but was not detected in normal thymus, spleen, liver, or other tissues. The partially purified material produced a massive fat mobilization when injected into normal mice.     

Selective,reversible inhibition of the lactose phosphotransferase system of Staphylococcus aureus by dodecyl sulfate and deoxycholate

Low concentrations of sodium dodecyl sulfate (0.015%) and sodium deoxycholate (0.33%) completely inhibit phosphorylation of β-galactosides by the lactose phosphotransferase system of Staphylococcus aureus. Inhibition is reversible, even after prolonged detergent treatment. Phosphorylation of methyl-α-glucoside by the same preparations is only slightly inhibited by 0.015% dodecyl sulfate. The membrane-bound component, Enzyme IF^lac, is not solubilized by 0.015% dodecyl sulfate, nor is its ability to bind [¹⁴C]lactose affected. The results are consistent with hypotheses of selective binding of anionic detergent to Enzyme II^lac or to Factor III^lac, the detergent serving in the latter case as a membrane analog.     

Expression of the phage λ recombination genes exo and bet under lacPO control on a multi-copy plasmid

The bacteriophage λ genes exo and bet, whose products (λ exonuclease and β protein, respectively; Red phenotype) mediate homologous recombination of λ phages, have been cloned under lacPOlacI^q control on multi-copy plasmids. Induction of recA3 cells harboring these plasmids with isopropylthiogalactoside (IPTG) resulted in λ exonuclease levels (assayed in vitro) that were proportional to the time of induction (for at least 4 h); recombination of λ Red^? phages in vivo was similarly inducible. Only one out of 25 bet^Δ plasmids (constructed by a variety of in vitro techniques) expressed λ exonuclease, a result consistent with the polarity of several known phage bet mutations. A general method for transferring phage exo and bet mutations to plasmids was devised and plasmids bearing polar (bet3) and nonpolar (bet113) mutations were constructed. Mutant derivatives of the plasmid showed the same complementation pattern as analogous phage red mutants. When λbet3 phages (Exo^?Bet^?) infected IPTG-induced recA3 bacteria containing exo⁺bet⁺ plasmids, recombination frequencies were no more than twice those typical for infection of plasmid-free recA3 cells with exo⁺bet⁺ phages, even in the case of IPTG induction sufficient to elevate the production of λ exonuclease about 100-fold. Even when plasmid induction was delayed till as late as 50 min after infection, recombination was significant. Preliminary experiments suggest that these plasmids encode a polypeptide with Gam activity that corresponds to the 98-amino acid “shorter” open reading frame assigned to gam by Sanger et al.     

Increasing viscosity of E. coli chromatin with increasing shear

We have observed that the viscosity of a solution of E. coli chromatin increases as the shear to which the solution is subjected is suddenly increased. This dilatant effect is opposite to the usual thixotropic non-Newtonian effects that are observed in DNA solutions. We suggest that the observed dilatancy may be explained in terms of shear-induced aggregation of large DNA molecules. Conditions for aggregation are discussed in the context of the “cluster theory” of condensation.