Compartmentation of the nucleolar processing proteins in the granular component is a CK2-driven process.

To analyze the compartmentation of nucleolar protein complexes, the mechanisms controlling targeting of nucleolar processing proteins onto rRNA transcription sites has been investigated. We studied the reversible disconnection of transcripts and processing proteins using digitonin-permeabilized cells in assays capable of promoting nucleolar reorganization. The assays show that the dynamics of nucleolar reformation is ATP/GTP-dependent, sensitive to temperature, and CK2-driven. We further demonstrate the role of CK2 on the rRNA-processing protein B23. Mutation of the major CK2 site on B23 induces reorganization of nucleolar components that separate from each other. This was confirmed in assays using extracts containing B23 mutated in the CK2-binding sites. We propose that phosphorylation controls the compartmentation of the rRNA-processing proteins and that CK2 is involved in this process.

hrp genes of Erwinia chrysanthemi 3937 are important virulence factors.

We developed improved virulence assays for Erwinia chrysanthemi 3937 on African violet varieties and devised a new method for the construction of precise bacterial gene knockouts. These methods were tested by constructing mutations in genes suspected to be involved with plant interactions. The virulence of the hrpG and hrcC mutant strains (both gene products presumed to be involved in protein secretion) was greatly reduced on leaves of semitolerant African violet varieties. An hrpN mutant strain produced delayed symptoms on African violet leaves and an hrpN delta pel (delta pel = five major pectate lyase genes deleted) double mutant was nonpathogenic. The hrcC and hrpG mutants did not produce a rapid hypersensitive response (HR) in tobacco, unlike the wild-type bacterium, and the hrpN mutant gave a reduced HR. The results, therefore, establish the importance of hrp genes in the virulence of E. chrysanthemi and their ability to elicit HR on nonhosts. The data also suggest that other effector proteins secreted by the Hrp system are required for full virulence and HR elicitation.

PCP4 is highly expressed in ectoderm and particularly in neuroectoderm derivatives during mouse embryogenesis.

PCP4 (PEP-19) belongs to a family of proteins involved in calcium transduction signals and binds calmodulin via an IQ motif, in a calcium independent manner. PCP4 gene maps to murine chromosome 16 and in human to chromosome 21. Murine PCP4 expression in the brain has been detected by Northern blot analysis to be mainly post-natal and in the adult to have a neuronal pattern. To investigate if it might have a role earlier in development, we analyzed its expression during mouse embryogenesis by in situ hybridization from E7.5 post-coitum (p.c.) to E17.5 p.c., and in P0 brain. Early, at E7.5, a high expression is restricted to the extra embryonic ectoderm. Embryonic expression starts at E9.5. At E10.5, PCP4 shows a strong signal in the post-mitotic cells of the diencephalon, the metencephalon and the myelencephalon and in the dorsal and cranial ganglia. The floor plate is also densely labelled. At E17.5, PCP4 is expressed in the central nervous system, in the myenteric plexus, and in other ectoderm derivatives, for instance the lens, the hairy cells of the cochlea, the enamel organ and the hair follicles. Thus, during embryogenesis PCP4 is mainly expressed in ectoderm and neuroectoderm comprising neural crest derived cells.