Polysome-ribosome distribution in isogenic RCstr and RCrel strains of Escherichia coli

AbstractStudy of the relative proportions of ribosomes and polysomes released by a standardized lysing procedure from isogenic RCstr and RCrel strains of Escherichia coli shows that a 20-min period of amino acid starvation of RCstr bacteria reduces the fraction of ribosomes recovered in polysomes to about 60% of its value characteristic of exponentially growing cells: A similar starvation treatment of the RCrel bacteria causes no appreciable reduction in the fraction of polysomal ribosomes

The Polycomb Protein and E3 Ubiquitin Ligase Ring1B Harbors an IRES in its Highly Conserved 5′ UTR

Ring1B is an essential member of the highly conserved Polycomb group proteins, which orchestrate developmental processes, cell growth and stem cell fate by modifying local chromatin structure. Ring1B was found to be the E3 ligase that monoubiquitinates histone H2A, which adds a new level of chromatin modification to Polycomb group proteins. Here we report that Ring1B belongs to the exclusive group of proteins that for their translation depend on a stable 5′ UTR sequence in their mRNA known as an Internal Ribosome Entry Site (IRES). In cell transfection assays the Ring1B IRES confers significantly higher expression levels of Ring1B than a Ring1B cDNA without the IRES. Also, dual luciferase assays show strong activity of the Ring1B IRES. Although our findings indicate Ring1B can be translated under conditions where cap-dependent translation is impaired, we found the Ring1B IRES to be cap-dependent. This raises the possibility that translational control of Ring1B is a multi-layered process and that translation of Ring1B needs to be maintained under varying conditions, which is in line with its essential role as an E3 ligase for monoubiquitination of histone H2A in the PRC1 Polycomb protein complex

Replication control of the Staphylococcus aureus chloramphenicol resistance plasmids pC223 and pUB112 in Bacillus subtilis.

A detailed physical and functional map of the chloramphenicol (Cm) resistance plasmid pC223 from Staphylococcus aureus was compiled. The plasmid's basic replicon and origin of replication were located and their nucleotide sequences determined. Two small RNAs of 92 and 155 nt, demonstrated by in vitro transcription with vegetative Bacillus subtilis RNA polymerase, were depicted as copy number regulating (cop) and incompatibility (inc) functions in Bacillus subtilis. pC223 and pUB112, another S. aureus Cm resistance plasmid, which exhibits marked sequence homology with pC223 and codes also for two small copRNAs, could be classified as members of the pT181-plasmid family (1). Copy numbers and segregational instability of pC223, pUB112 and deletion derivatives of both in B. subtilis showed great differences despite of their homologous basic replicons