TABLE 2.

Mutations of MA sequences important for Mo-MLV replication show defects in pre-B-cell transformation by Ab-MLV^a

Virus	Expt 1		Expt 2
	Frequency	Day(s)	Frequency	Day(s)
P120	5/5	8, 9	7/7	8, 9
G2A	0/4	_b	1/7c	26
54-56A	3/5	11, 13	1/7	32
60-62A	3/5	11, 14, 16	1/7	13
69-71A	5/5	9	7/7	8
85-87A	3/5	12, 14	2/7	16, 30
111-115A	NTd	NT	7/7e	8

^aThe frequency of transformation was assayed by infecting bone marrow cells with undiluted virus stocks of similar titers and plating them in liquid medium. Cell cultures were scored as transformed when the density of transformed lymphoblastoid cells reached 2 × 10⁶ cells/ml. Frequency values indicate the numbers of transformed cultures/total number of cultures examined. Day(s), day(s) postinfection when the cultures were scored as transformed. Unless otherwise indicated (see footnote e), data shown are representative of the results of at least three independent experiments.

^bNo evidence of transformation was found during the entire observation period of approximately 40 days.

^cAn additional 10 samples were evaluated with the G2A mutant in an experiment independent from those whose results are represented in the table. None of these G2A-infected cultures gave rise to transformants.

^dNT, not tested.

^eA total of 17 dishes were evaluated for this virus in two independent experiments. The second experiment, in which 10 dishes were evaluated, was conducted independently from the experiments shown in the table. All 10 of the dishes were transformed in 7 to 9 days.