In considering our discussion further on the penicillin studies, I think we overlooked the results of several previous experiments
which throw a new light on the latest results. Both Bruce and I have consistently observed that the addition of at 120 immediately
following DNA addition leads to no decrease in the absolute no. of transformants over what one obtains if no penicillin is
added. Therefore, it seems to me that there cannot be both a cyclical competency and no effect of DNA on conferrinig penicillin
resistance. For the cells which have picked up DNA at 90-120 (DNase then added) must be the same cells which are resistant
at 150, and indeed resistant up to 270 after DNA addition. Since DNase is added at 120, there can be no balance between killing
of "old" transformants and the appearance of "new" transformants.
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The original picture that Bruce and I came up with was that competent cells have best the ability to multiply at the time
they reach maximal competence. These same cells further do not begin to multiply until about 4 hr. after DNA add'n.
I think the data now indicate that cells maximally competent are resistant to penicllin before DNA add'n (and 30 min.
before maximal competence they are 10 x as sensitive compared to the whole population). These competent cells can behave
in 2 ways. If DNA is not added, they go through cycles of competency, and coincidentally penicillin sensitivity and resistance.
But, the integration or some related phenomenon of DNA interaction with the recipient cells stabilizes the penicillin resistance,
presumably by inhibiting cell multiplication.
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The most confusing area in the picture is where we haven't been able to demonstrate penicillin resistance of a portion
of the entire population when transformants specifically haven't been studied (but DNA is added). I suspect that perhaps
this negative finding could be explained by assuming a very heterogeneous recipient population, and specific requirements
for penicillin resistance, presumably those necessary for transformation.
I think it might be worthwhile to try Spizen's[?] procedure for competency, thereby giving a different recipient population
as judged by the number of unlinked double transformants. Perhaps resistance could be demonstrated under these conditions.
Certainly we shall have to do more experiemnts to try and determine whether we can show it under
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conditions of penicillin killing > 99%.
It looks like another rain-free, sunny day at the park. We were planning on making a 10 mile bike, but the maxim of "Early
to bed... doesn't seem to hold for Indians and some women. So I doubt that we'll get more than a few miles.
Mar and I are both quite anxious to return, since there are many obvious experiments to do (and competitors who are trying
to do them).
I was told by Kozinska that Harriet has stopped his annealing experiments. Apparently he was trying to get a third linked
marker (or maybe unlinked) into his system and found that his 2 linked marker system wasn't behaving anymore.