March 30, 1973
Dear Dan,
This note will reach you via Michel. We have now checked the enzyme (using the conditions specified in your letter) and the 32P-autoradiographs of the gel look just fine. So not too much activity can have been lost. Nonetheless, I would be grateful for a further small sample (what you can spare) of the H. influenzae and, of course, the parainfluenzae enzyme.*
Many thanks also for the preprints, which I read with great interest, as also your two papers in the last issue of Virology. By reassociation kinetics (cot shifts of labelled serially passaged DNA by excess cold parental DNA) we have now revised our former estimate of the extent of the host substitution; in the third passage progeny, 45% of the sequences appear to be nonviral. Since only 10% of the sequences behave as repetative cell DNA in the filter assay of the same material **, we are assuming that 30% is most probably non-repetative cell DNA. We have another set of serial passages which is turning out, I think, to be rather similar to the one described by you.
With best regards from all of us,
Yours,
Ernest
*Michel is willing to bring the sample back with him.
**H. influenzae fragments.