Prescott: Stylonychia

Date:
1972
Reference:
PP/CRI/H/5/6
Catalogue details

Licence: In copyright

Credit: Prescott: <i>Stylonychia</i>. Source: Wellcome Collection.

    1/25
    Dear Dr. Pre Scott, Thank you for the preprint describing your studies on Stylonichia. I was delighted to receive this as Sydney Brenner had told me about your work. The results are certainly very challenging, though their implications baffle me. At first sight one would conclude that the majority of the DNA is there to assist pairing in meiosis, but Í am reluctant to think this is its only function. There is one aspect of your paper which I should like to ask you about. You state that the kinetic complexity of the macronuclear DNA is about 20 times E_. coli, suggesting a figure of about 6 x 10^ base-pairs. The average length of the molecules is 0.75[j, correspond ing to about 2200 base-pairs. Thus one might expect that it consisted of about 27,000 different molecules. One naturally wonders whether this is approximately equal to the number of bands one sees in the polytene material. Is it possible to make a rough estimate of this number by trying to count them? Another approach would be to obtain a figure for the absolute amount of DNA in a single cell, so that figure 2 could be put on an absolute scale. If one -could then estimate approcimately the absolute amount of DNA in anaverage band, by cytophotometry, this would also give a figure for the total number of bands. In short, if one adopts the hypothesis that one (type of) DNA mole cule in the macronucleus comes from one band in the polytene chromo somes, is there any numerical evidence to support the idea? I should also like to ask about histones in Stylonychia. Sydney tells me that you think histones are present. Is this correct? If so, can one make any estimate of their amount? In particular, does the macronucleus show any signs of having histones, (and, if so, how much in relation to the DNA?) or are they confined to the micronucleus. continued/