Nucleic Acids Research, 1984, Vol. 12, No. 23 9009-9023
© 1984
MOLECULAR BIOLOGY |
Lysine tRNA and cell division: A G1, cell cycle mutant is temperature sensitive for the modification of tRNA5Lys to tRNA4Lys
Department of Biochemistry and Ophthalmology and the Division of Biological Science, University of Missouri Columbia, MO 65211, USA
Received July 27, 1984. Revised November 5, 1984. Accepted November 5, 1984.
Ts-694 is a temperature sensitive mutant of hamster cells which is blocked in the G1 phase of the cell cycle at the restrictive temperature of 39°. A comparison of the Lys-tRNA isoacceptors by RPC-5 chromatography showed a decrease in 
and an increase in 
, at 39°. This was identical to the changes seen in confluent cultures at the permissive temperature of 33°. These Lys-tRNA changes were not seen in ts-694 cells blocked in G1 by isoleucine deficiency, nor in two other G1 ts mutants at the restrictive temperature. Cells trapped in S phase by a thymidine block also contained decreased levels of when raised to 39°. Both levels and cell division increased when the cells were returned to the permissive temperature.
An in vitro assay was established for the modification of to with 
and 
as intermediates. The first reaction is the synthesis of which involves the introduction of a modified uridine at the third position of the anticodon. Extracts of 694 cells growp t 33° were able to modify rat liver [3H] to and in vitro when assayed at 25° but not at 39°. Extracts of Balb/c 3T3 cells, however, were more active at 39° than at 25° showing that the normal enzyme is not temperature sensitive. Ts-694 cell tRNA, isolated from cells grown at 33Lys was aminoacylated at both 25°and 39° with rat liver synthetases. was present at both temperatures indicating that ts-694 cells do not contain a temperature sensitive .