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.