Amino acid induced changes of puffing patterns in Chironomus salivary gland chromosomes

Studies on the effects of neomycin on puffing in Chironomus

Fourth instar Chironomus sp. larvae were used. Isolated salivaries (1/2) were incubated in RINGER containing various amounts of neomycin sulphate for various durations. Another half of salivaries, incubated in RINGER for corresponding durations served for controls. for in vivo experiments larvae were exposed to distilled water containing neomycin. Analysis of squashed preparations has revealed that puffing varies with incubation period in in vitro experiments with low concentration of drug. In in vivo studies also puff induction was evident. Higher concentrations of neomycin both in in vivo or in vitro treatments disorganized chromosomes. Present results suggest that neomycin can activate genes in an insect (or in other words in eukaryotes).

Inhibition by tryptophan of nucleolar RNA synthesis in salivary gland nuclei of Chironomus thummi

Tryptophan, but not glutamine and lysine, inhibits the incorporation of 3H-uridine into nucleoli of explanted salivary glands by about 60%. In isolated nuclei also, the nucleolar incorporation of 3H-uridine triphosphate is reduced to about 50% by tryptophan. It is concluded that tryptophan acts directly at the nuclear level and the possible mechanisms.

The control of puffing by ions - the Kroeger hypothesis: a critical review

We have re-examined the several papers which appear to us to represent the principal lines of evidence for what we call the Kroeger hypothesis. To do this we have stated this hypothesis in its simplest, most concrete form, a form that has been repeatedly and forceably enunciated in the literature (Kroeger, 1963a, 1965, 1966, 1967, 1968; Kroeger and Lezzi 1966; Lezzi and Frigg, 1971). The evidence suggests to us that ecdysone's effect on puffing is probably not mediated by the [K+]/[Na+]. While such a model cannot, even now, be excluded, we see little reason to believe in it. We take the general issues raised by Kroeger's ideas very seriously. Nucleoprotein complexes are exquisitely sensitive to changes in salt concentration and ionic selectivity is a well-known property of proteins (and of ion-exchangers in general, see, for example, Diamond and Wright, 1969). Thus it might not be shocking if cells utilized this specificity in some general control over chromsosome structure, perhaps a second-layer of control superimposed upon other transcriptional controls. Therefore it is our feeling that Kroeger's data merits very careful and critical study, the more so because the experiments involved are intrinsically difficult. It is in this vein that we have tried to review Kroeger's data.