A cellular gene encodes scrapie PrP 27-30 protein

Bacteriophage MS2 RNA is 3,569 nucleotides long. The nucleotide sequence has been established for the third and last gene, which codes for the replicase protein. A secondary structure model has also been proposed. Biological properties, such as ribosome binding and codon interactions can now be discussed on a molecular basis. As the sequences for the other regions of this RNA have been published already, the complete, primary chemical structure of a viral genome has now been established.

Complete nucleotide sequence of bacteriophage MS2 RNA: primary and secondary structure of the replicase gene.

Purification of the DNA Polymerase of Avian Myeloblastosis Virus

The rpoS-encoded cr s subunit of RNA polymerase in Escherichia coil is a global regulatory factor involved in several stress responses. Mainly because of increased rpoS translation and stabilization of cr s, which in nonstressed cells is a highly unstable protein, the cellular ~r s content increases during entry into stationary phase and in response to hyperosmolarity. Here, we identify the hfq-encoded RNA-binding protein HF-I, which has been known previously only as a host factor for the replication of phage Q~ RNA, as an essential factor for rpoS translation. An hfq null mutant exhibits strongly reduced ~r s levels under all conditions tested and is deficient for growth phase-related and osmotic induction of ~r s. Using a combination of gene fusion analysis and pulse-chase experiments, we demonstrate that the hfq mutant is specifically impaired in rpoS translation. We also present evidence that the H-NS protein, which has been shown to affect rpoS translation, acts in the same regulatory pathway as HF-I at a position upstream of HF-I or in conjunction with HF-I. In addition, we show that expression and heat induction of the heat shock ~r factor cr 32 (encoded by rpoH) is not dependent on HF-I, although rpoH and rpoS are both subject to translational regulation probably mediated by changes in mRNA secondary structure. HF-I is the first factor known to be specifically involved in rpoS translation, and this role is the first cellular function to be identified for this abundant ribosome-associated RNA-binding protein in E. coli.

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The RNA-binding protein HF-I, known as a host factor for phage Qbeta RNA replication, is essential for rpoS translation in Escherichia coli.

Publisher Summary This chapter explains and interrelate the results of studies on the structure and functions of S1. This chapter discusses various structure such as amino-acid sequences, four repeating homologous stretches, and secondary structure elements. Several methods have been developed to gain information on the relative positions of individual ribosomal components in situ and thus to obtain the molecular topography of the ribosomal particle. These methods include: (a) cross-linking of neighboring components by means of chemical cross-linking agents or by photoactivation; (b) immunoelectron microscopy— that is, visualization of a component on the image of the ribosome by the means of its specific antibody; and (c) the neutron scattering procedure using ribosomes containing deuterated components. All these procedures have been applied in the case of S1, but the results have not been fully satisfactory. There are two r-proteins that have clear functional roles in protein biosynthesis: S1 on the small ribosomal subunit and L7/L12 (the dimorphic protein) on the large subunit. Together on the ribosome, they amount to 110,000 daltons or over one-eight of the r-protein mass. They are also the best studied of all r-proteins. The structure, function, and evolution of L7/L12 have been described, and the structure and homology relationships of a chloroplast L12 protein are discussed in this chapter.

Structure and functions of ribosomal protein S1.

Qβ replicase comprises four different polypeptides, only one of which is coded for by the phage genome.

R. Gallerani

Papers

Subunit structure of Q-beta replicase.