Dependence of Balbiani ring puffing on protein synthesis

The possible dependence of puffing of the Balbiani rings (BRs) on the protein synthesis has been investigated by studying the response of these structures to protein synthesis inhibition induced by cycloheximide and anisomycin. When larvae of Chironomus thummi belonging to middle IV instar (BR1 repressed, BR2 expanded) are subjected to short treatment (3--6 h) with these drugs, BR1 and BR2 puffing states remain essentially unaffected. But when the same treatments are applied to galactose-pretreated larvae (BR1 expanded, BR2 repressed), selective reactivation of the collapsed BR2 occurs. These observations suggest that maintenance of a given puffing state can be dependent, to a variable extent, on the supply of newly synthesized proteins. In particular, selective re-expansion of galactose-repressed BR2 induced by the drugs seem to indicate the existence of repressor-like factor whose activity would be triggered by the galactose treatment.