26 November 1958
Dear Paul,
First let me thank you for the details of how you prepare soluble RNA. I have still not had the chance to try this, and there is such a little time left to me now that I shall have to stick to rats, which is a pity.
We were all very intrigued by the cryptic sentence in your first letter about RNA which would take up only one amino acid but which was not homogeneous. This has been interpreted here in two ways. First, and more likely, that you have "knocked out" all the other soluble RNA chains, for example by labeling with one amino acid only, and then reacting with periodate (I have done one experiment which shows that attached amino acids do indeed protect the soluble RNA against the action of periodate). Second, that you have obtained a sample in which all your RNA chains take up one sort of amino acid, and one sort only, but that the chains are not all identical. This, as you may remember, is what I expect to be the case (that is, that they are identical only near the operative end) but I suspect this is not what you meant.
I am still trying to obtain a sample of RNA whose chains only take up Tyrosine. I have a diazo column which removes all, or almost all the Tyrosine - RNA (that is, the RNA which passes through the column, takes up numerous amino acids but not tyrosine) but I have not yet succeeded in getting the Tyrosine-RNA off the column, though I am still trying. I am still hoping I may succeed before I leave for the States.
I am writing separately to Ofengand about his fellowship application. Perhaps you could show him this letter so that I don't have to repeat myself.
We are still hoping to be in California in July, so perhaps we shall meet there, if not before.
With best wishes,
Yours ever,
Francis