B. WRIGHT: No, I showed that G-6-P stim- 

 ulated at low UDPG not high UDPG. This 

 doesn't make the enzyme different. All I said 

 was that the combination of increasing G-6-P 

 and UDPG would enter into their effect on cell 

 wall synthesis; and if the UDPG level happened 

 to be unusually low, the G-6-P would stimulate 

 the cell wall synthesis more. This is not in- 

 volved in the reaction although it's a modifier. 

 It stimulates cell wall synthesis more when 

 UDGP is low, no matter what stage the enzyme 

 is taken from. 



PAPACONSTANTINOU: No matter what 

 stage you take this enzyme from you always 

 get the same reaction? 



B. WRIGHT: Right. 



GRUN: Am I wrong in thinking that this 

 organism at the time that it is aggregating is 

 a syncytium? 



B. WRIGHT: That's wrong. There are in- 

 dividual cells. 



FERGUS: There's still one nucleus per 

 cell. 



TS'O: I think that the kind of differentia- 

 tion process which I have in mind is different 

 from what you have described. For instance, I 

 could pose a decision-making process like that 

 in the determination of sex. Once the decision 

 is made, the organism will carry this decision 

 to its grave. That decision is made in the early 

 cell and you cannot change it. 



B. WRIGHT: I don't think you can consider 

 such complex examples if we're going to talk 

 about it. This is why I introduced the talk by 

 saying morphogenesis is a change in structure; 

 therefore, we can look for a simple example 

 that we can talk about. A lot of biologists like 

 to talk and think in such complex terms about 

 morphogenesis, it's difficult to analyze it. 



GROSS: Are there any specific differences 

 where you can find rate-limiting reactions or 

 something that does one thing that does give 

 control such as induction in E. colt? 



B. WRIGHT: UDPG is limiting, soisG-6-P, 

 and several other things here are also limiting. 

 If you studied one of them alone, it might look as 

 though you'd found the answer. 



GROSS: The general trend of what you're 

 saying is that epigenetic considerations may be 

 more central to differentiation than genetic ones. 



B. WRIGHT: No, if you don't have the gene, 

 you don't have the enzyme. All I'm saying is that 

 if you want to know what the immediate control 

 of this process is, it may or may not be genetic: 

 you may have gotten the synthesis of the relevant 

 enzyme a long time ago; you may already have 



the enzyme, or at least the message for it. In 

 glutamic acid dehydrogenase you have the en- 

 zyme throughout the differentiation, but it be- 

 comes 7 times more active when it gets more 

 endogenous substrate. This is another thing I 

 think ought to be stressed to clarify the situa- 

 tion. What we are talking about when we say: 

 this is essential; this is important. This is one 

 minor cause here, and we're just beginning to 

 clearly see that you may have a lot of causes 

 at one time. You know before a particular dif- 

 ferentiation process, for example, you've got 

 templates. They are one kind of cause. Now, 

 where does the immediate control lie? Maybe 

 it's on the activation of the message. Maybe 

 that's not it at all. Maybe the enzyme is syn- 

 thesized all the time and it simply accumulates 

 because the substrate is stabilizing. There 

 could be other explanations, and are probably 

 many of them. 



TILL: Am I right that you're arguing that 

 what you've studied is all an inevitable con- 

 sequence of the starvation? 



B. WRIGHT: We know that definitely; if it 

 gets fed, it doesn't differentiate. 



TILL: Then the decision is whether or not 

 it gets hungry. 



CHALKLE Y: It' s the concept of differentia- 

 tion that we're mixing up. Differentiation at the 

 epigenetic level defined in terms of morpho- 

 logical changes. One of you is talking about that 

 and one of you is talking about genetic control 

 in an already differentiated system. 



B. WRIGHT: They're both essential and we 

 should just define which one we're talking about. 

 I think it's important to stress that there is no 

 one important thing here at all. 



FERGUS: I don't think that fruiting neces- 

 sitates starving because you can obtain fruits 

 right on the same plate with a large supply of 

 bacteria still present. 



B. WRIGHT: Yes, but they're not eating it. 



FERGUS: Well, if they aren't eating, there 

 must be some other factors, then, that prevent 

 their ingestion, rather than that they're being 

 starved. They're not being starved; they're 

 already full of bacteria. 



B. WRIGHT: When they're aggr eating, 

 they are essentially starving. They'll do the 

 same thing whether you have them on nutrient 

 agar or 2% agar. An important factor in their 

 starvation may be that the permeability is ter- 

 rible in these amoebae. The permeability for 

 some compounds is l/20th as good in the amoeba 

 as it is at culmination; by that time you can't 

 interest them at all in eating. 



120 



