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A number of strains of Abelson murine leukemia virus (A-MuLV) with various abilities to transform cells have been identified. Among these is the A-MuLV-P90 strain, a mutant derived from A-MuLV-P120 that encodes an A-MuLV protein missing sequences that are normally present at the extreme carboxy terminus of P120 (N. Rosenberg and 0. N. Witte, J. Virol. .33:340-348, 1980). This virus transforms NIH 3T3 cells efficiently but does not transform a high frequency of lymphoid cells in vitro or in vivo. In this communication, we show that of the relatively few tumors induced by A-MuLV-P90 nearly all contained new variant viruses that stably expressed either larger or smaller A-MuLV proteins. Strains that expressed larger A-MuLV proteins behaved like A-MuLV-P120 in transformation assays, whereas those expressing smaller A-MuLV proteins induced a high frequency of tumors after a short latent period in vivo but failed to transform large numbers of lymphoid cells in vitro. Thus, these latter viruses separated the requirements for in vitro transformation of lymphoid cells from those for tumor induction. All of the variants differed from A-MuLV-P90 in the carboxy-terminal region of the A-MuLV protein, suggesting that sequences in this region play a key role in the ability of the virus to interact with hematopoietic cells in vivo and in vitro.

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Assay of tannase activity was performed directly, using extracts of black tea leaf, by a pH stat method at the pH optimum of the enzyme (6.0). Reaction rates were calculated from the initial rates of the volume of titrant vs. time plots, and activity was expressed as pmoles/min. The enzyme was unstable to pH levels above 6.0 and temperatures above 40°C. Optimum temperature was 35°C. Using saturating amounts of enzyme, the pH stat was also used to determine total hydrolyzable gallate for kinetic studies and to determine the effect of gallated polyphenols on loss of solids in instant tea processing.