The organs of a higher plant show two fundamental axes of asymmetry: proximodistal and dorsoventral. Dorsoventrality in leaves, bracts, and petal lobes of Antirrhinum majus requires activity of the PHANTASTICA (PHAN) gene. Conditional mutants revealed that PHAN is also required for earlier elaboration of the proximodistal axis. PHAN was isolated and shown to encode a MYB transcription factor homolog. PHAN mRNA is first detected in organ initials before primordium initiation. The structure and expression pattern of PHAN, together with its requirement in two key features of organ development, are consistent with a role in specifying lateral organ identity as distinct from that of the stem or meristem. PHAN also appears to maintain meristem activity in a non-cell-autonomous manner.

Sensory organ formation in Drosophila is activated by proneural genes that encode basic-helix-loop-helix (bHLH) transcription factors. These genes are antagonized by hairy and other proline-bHLH proteins, hairy has not been shown to bind to DNA and has been proposed to form inactive heterodimers with proneural activator proteins. Here, we show that hairy does bind to DNA and has novel DNA-binding activity: hairy prefers a noncanonical site, CACGCG, although it also binds to related sites. Mutation of a single CACGCG site in the achaete [ac) proneural gene blocks hairy-mediated repression of ac transcription in cultured Drosopbila cells. Moreover, the same CACGCG mutation in an ac minigene transformed into Drosopbila creates ectopic sensory hair organs like those seen in bairy mutants. Together these results indicate that hairy represses sensory organ formation by directly repressing transcription of the ac proneural gene.

An 8.2 kb fragment of E. coli chromosomal DNA, when cloned in increased copy number, suppresses the dnaA46 mutation, and an abundant protein of about 68 kd (60 kd when measured by us), encoded by the fragment, is essential for the suppression (Takeda and Hirota 1982). Mapping experiments show that the fragment originates from the 94 min region of the chromosome. It encodes several proteins but only one abundant polypeptide of the correct size, the product of the groEL gene. Suppression by the fragment is allele specific; those mutations which map to the centre of the gene are suppressed. Other initiation mutants including dnaA203, dnaA204, dnaA508, dnaAam, dnaC, dnaP and dnaB252 are not suppressed. Most suppressed strains are cold-sensitive suggesting an interaction between the mutant proteins (or their genes) and the suppressing protein or proteins.

Calmodulin, a primary plant calcium receptor, is known to be intimately involved with gravitropic sensing and transduction. Using the calmodulin-binding inhibitors trifluoperazine, W7 and calmidazolium, gravitropic curvature of Arabidopsis thaliana (L.) Heynh, ecotype Landsberg, roots was separable into two phases. Phase I was detected at very low concentrations (0.01 microM) of trifluoperazine and calmidazolium, did not involve growth changes, accounted for about half the total curvature of the root and may represent the specific contribution of the cap to gravity sensing. Phase II commenced around 1.0 microM and involved inhibition of both growth and curvature. The agr-3 mutant exhibited a reduced gravitropic response and was found to lack phase I curvature, suggesting that the mutation alters either use or expression of calmodulin. The sequences of wild-type and agr-3 calmodulin (CaM-1) cDNAs, which are root specific were completely determined and found to be identical. Upon gravitropic stimulation, wild-type Arabidopsis seedlings increased calmodulin mRNA levels by threefold in 0.5 h. On the other hand, gravitropic stimulation of agr-3 decreased calmodulin mRNA accumulation. The possible basis of the two phases of curvature is discussed and it is concluded that agr-3 has a lesion located in a general gravity transmission sequence, present in many root cells, which involves calmodulin mRNA accumulation.

The pcnB gene product of Escherichia coli is required for copy number maintenance of plasmids related to ColEl and also for that of the IncFII plasmid R1. Because PcnB is similar to the tRNA-binding protein tRNA nucleotidyltransferase, we have suggested that the protein would be required only for processes in which an RNA is a prominent regulatory component. This appears to be so; strains deleted for pcnB, although defective in ColEl and R1 plasmid maintenance, maintain the iteron-regulated plasmids F and P1 normally. We also find that strains deleted for pcnB grow normally, demonstrating that PcnB has no essential cellular role under the conditions tested and suggesting that regulation by antisense RNAs similar to RNAI has no critical role in any essential host process. We confirm by immunological tests that PcnB is likely to be the commercially available enzyme poly(A) polymerase.The Eschenchia coli pcnB gene product is required for normal copy number maintenance of plasmids related to either ColEl or R1 (13, 14, 16, 17). Replication frequency in each of these plasmid groups is controlled, in part, by an antisense RNA (for a review, see reference 5). RNAI binding prevents productive folding of the ColEl replication primer, while copA RNA prevents translation of the message for the essential R1 replication protein, RepA. PcnB shares homology with the product of the E. coli cca gene, tRNA nucleotidyltransferase, a protein which binds tRNA (17). It has therefore been suggested that PcnB may also be an RNAbinding protein and may expedite plasmid replication by interfering with the inhibitory sense-antisense RNA interactions which limit it. Although several host processes have been described in which RNA interactions are believed to affect gene expression (for reviews, see references 6 and 26), none of these appear to be of critical importance to the cell, and it is thus possible that the principal role of PcnB is the modulation of plasmid replication. To investigate this question further, we have constructed a strain from which the pcnB gene has been deleted and report its properties here. We find pcnB to be a dispensable gene. MATERIALS AND METHODSBacterial strains, plasmids, and genetic techniques. The bacterial strains used are described in Table 1. Linear transformations were performed as described previously (25). The plasmids used in curing experiments, pBR325, the mini-R1 plasmid pGW71, the mini-F plasmids pSC138, pXX325, and pXX327, the mini-P1 plasmids pAX274 and pAX275, and pRE1-1, in which pcnB is expressed from a A PL, are also described in Table 1. pRE1-1 is maintained in MZ1, which is lysogenic for XcI857. Plasmids used for fusion protein production are described below. Other transformations, transductions, and conjugations were performed by using standard techniques, and media used were as previously described (19). Antibiotic concentrations used for routine growth were as follows: ampicillin, 10 ,ug/ml (mini-F * Corresponding author. and mini-P1 plasmids) or 50 ,ug/ml (ColEl-based plasmids); tetrac...