Biomedical subjects
H Berliner
Publications and source records attributed to H Berliner.
Binding of tRNA to reverse transcriptase of RNA tumor viruses.
The interaction of tRNA with the reverse transcriptase (RNA-dependent DNA polymerase) of mammalian RNA viruses, such as Moloney murine leukemia virus and simian sarcoma virus, has been studied. Whereas the purified reverse transcriptase of mammalian viruses sedimented in glycerol gradients as a globular protein with a molecular weight of 70,000, after interaction with tRNA the enzyme cosedimented with a protein of 150,000 molecular weight. The twofold increase in molecular weight could be a result of either two reverse transcriptase molecules complexed with a tRNA or, alternatively, several tRNA molecules bound to a single enzyme polypeptide. The enzyme complexes were dissociated in part upon degradation of the tRNA moiety by pancreatic RNase A. The reverse transcriptase released from virions of Moloney murine leukemia virus, simian sarcoma virus, and avian myeloblastosis virus, by nonionic detergent, migrated faster on glycerol gradients than purified enzyme preparation. This phenomenon was probably due to complex formation between part of the virion enzyme and the tRNA, which is endogenous in virions. Addition of exogenous tRNA was needed, however, to quantitatively complex all the virion reverse transcriptase of Moloney murine leukemia virus and simian sarcoma viruses. The reverse transcriptase of Moloney murine leukemia virus did not show tRNA species specificity in the binding reaction when glycerol gradients were used for assay. Thus, several tRNA species of Escherichia coli, yeast, chicken, and rat origin were able to complex with the enzyme. The species specificity in the interaction between tRNA and avian myeloblastosis virus reverse transcriptase was also examined. We demonstrated that under our experimental conditions, this enzyme binds different tRNA species of E. coli and yeast as well as tRNA of chicken origin.
Urea transport in the dogfish kidney.
There is increasing evidence that urea movement across many epithelia involves more than passive diffusion. Of particular interest is the observation that urea transport across the erythrocyte membrane and across the vasopressin-stimulated urinary bladder of the toad occurs by facilitated diffusion, and can be selectively inhibited by phloretin and chromate. These inhibitory agents have been employed in studies of renal urea reabsorption by the spiny dogfish Squalus acanthias. Both agents inhibit urea reabsorption; the effect of chromate is of particular interest, since it blocks urea reabsorption to a proportionately greater extent than sodium reabsorption, and does so irreversibly.
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