Communicated by J.H.Weil tant of Bradyrhizobiumjaponicum, the amounts of GS mRNA did not increase over that in roots. These experiments, together with the time course of increase in GS mRNA transcripts, suggest that the genes encoding cytosolic GS are directly induced by the available ammonia.

Control of gene expression in Euglena was examined during light-induced chloroplast development. Greening was achieved under standard conditions which allowed the synthesis of all plastid proteins in both cytoplasmic and chloroplastic compartments, or under experimentally modified conditions inducing the preferential synthesis of the photosystem II (PSII) light-harvesting antenna or reaction centers. The relative composition of total mRNAs in cellular, cytoplasmic or chloroplastic fractions, as analyzed by their in-vitro translation products in cell-free systems did not significantly change during the in-vivo protein-synthesis processes which are specific to each greening system. By contrast, cytoplasmic polysomal mRNAs extracted during the selective recovery phase of PSII light-harvesting antennae provided a major in-vitro synthesis product of 28 kDa which could correspond to a precursor of the main 26-kDa apoprotein of the light-harvesting chlorophyll a/b protein complex. Similarly, the in-vivo selective synthesis of the 41-kDa and 51-kDa polypeptides of PSII reaction centers was concomitant with an enrichment of plastid polysomes in mRNA species coding for polypeptides of the same molecular weight. These observations confirm that protein synthesis during chloroplast development in Euglena is weakly regulated at the transcription level and they demonstrate that translational regulation occurs in both the cytoplasmic and the chloroplastic compartments.

Phage +197 is representative of a widespread lactococcal phage group characterized by a particular morphology (prolate head with a noncontractile tail). In order to develop an immunoenzymatic phage detection test, fusion proteins containing 13-galactosidase fused to epitopes of phage +197 structural proteins were constructed by cloning random DNA fragments from the phage genome upstream of a lacZ gene on a plasmid vector. Recombinant plasmids containing certain fragments encoded the synthesis of fusion proteins which react with polyclonal antibodies against the phage and confer a Lac' phenotype on Escherichia coli. Three different epitopes were represented; phage-specific DNA fragments encoding these epitopes were mapped at three locations on the phage genome, and their nucleotide sequences were determined. Two fused phage antigens were conformational epitopes, whereas the phage epitope of protein encoded by the recombinant plasmid designated pOA17 was a denaturation-resistant epitope. This epitope was very immunogenic. Protein encoded by plasmid pOA17 was synthesized in large amounts from a strong promoter. Antibodies raised against this hybrid protein were used to identify the 46-kDa minor phage protein which provides the epitope. Antibody cross-reactivity of phages related to +197 showed that this epitope is well conserved in this genetic group.