300-305 PROTEINS; POLYPEPTIDES

$91

Biochemistry

SOME CHARACTERISTICS OF A CELL-FREE DNAase SENSITIVE SYSTEM
INCORPORATING AMINO ACIDS INTO PROTEIN. J. Heinrich Matthaei*™
and Marshall W. Nirenberg”. National Institutes of Health,
Bethesda, Md.

Extracts of E. coli W3100 prepared by grinding cells with
alumina actively incorporate Cl4-valine into protein. The
extracts were centrifuged at 20,000 x g for 20 minutes,
Remaining intact cells and debris were removed from the super-
natant suspension by centrifuging at 30,000 x g for 60 minutes.
Ribosomes were obtained by centrifuging the supernatant sus-
pension for 2 hours at 105,000 x g. For maximm incorporation
of Cl4-valine into protein reaction mixtures require ATP, Mg++
an ATP generating system, a complete amino acid mixture, ribo-
somes and a 105,000 x g supernatant solution. Incorporation
of cl4-valine into protein proceeds at a rapid rate for 15
minutes at 37°, Incorporation is markedly inhibited by 50 pg.
chloramphenicol per mi, 10 ug. per ml. DNAase inhibited
approximately 70% of the incorporation whereas an equivalent
amount of RNAase was completely inhibitory. Inhibition by
DNAase cannot be reversed by addition of polyanions. Addition
of a DNAase digest of salmon sperm DNA had no effect upon
incorporation of cl4.valine into protein. Although DNAase
markedly inhibits amino acid incorporation into protein, it
ia not known whether intact DNA is necessary for this process.