Sara Sarid

Bacteriophage Induced Transfer RNA in Escherichia coli

The events taking place after a viral nucleic acid enters a susceptible host cell depend on the specific viral system. In the case of the DNA-containing viruses (1), the nucleic acid serves as a template both for its own replication and for the transcription of viral specific mRNA which is then translated into viral proteins. It has been generally thought that the various components of the host translational system remain unaltered and are utilized for the synthesis of viral proteins; the viral mRNA becomes attached to the preexisting host cell ribosomes, and viral polypeptides are then synthesized by the preexisting host cell tRNA and aminoacyl-tRNA synthetases. This is a rather simplified presentation of the events taking place during synthesis of viral proteins. Recent experiments show that the picture may be more complicated, and, at least in the case of some viruses, a more intricate translational mechanism is involved. Studies from several laboratories show that mammalian and bacterial viruses may induce changes in the translational mechanism of their host cells. These changes were observed in the tRNA, in the enzymes modifying the tRNA (such as tRNA methylases and tRNA thiolases), or in the aminoacyl-tRNA synthetases. The evidence for changes in the translation mechanism which follow virus infection is summarized below. Several modifications of tRNA induced by virus infection have been observed. Thus, the chromatographic profile of leucine tRNA in Escherichia coli is altered after the bacterial cells have been infected with T2 bacterio-

Amino acid acceptor activity of bacteriophage T4 transfer RNA

In a recent study we have shown that T4 bacteriophage infection of E. coli B cells induces the formation of 4s RNA molecules that specifically hybridize with T4 DNA [1,2] . Moreover, the T4 4s RNA extracted from the hybrid was found to contain pseudouridylic acid [2]. Since IL UMP is believed to be present predominantly in transfer RNA, its presence in a 4S RNA molecule coded for by the T4 genome suggested that at least some of this RNA may have amino acid acceptor function. To test this hypothesis a method was devised to recover intact, biologically active tRNA from tRNADNA hybrids [3]. We recently reported that the T4 4S RNA preparation extracted from a hybrid with T4 DNA has amino acid acceptor capacity [4]. In addition, Weiss et al. [S] showed that leucyl-tRNA isolated from TCinfected cells will hybridize with T4 DNA. This report describes the method used for the isolation of biologically active T4 tRNA from its hybrid with T4 DNA.

Agrobacterium tumefaciens RNA in non-tumorous tomato cells

Abstract Agrobacterium tumefaciens , strain B6 (virulent), RNA has been found in non-tumorous tomato cells after the plants have been dipped in a bacterial suspension. The percentage of in vitro hybridization between the A. tumefaciens DNA and the RNA extracted from plants dipped in the bacterial suspension is higher than between this DNA and the RNA from bacteria grown in culture.

In vitro transcription of E. coli tRNA genes carried by transducing phages.

Transducing phages have proved very useful in studies involving specific bacterial genes carried by the phage DNA; because of their smaller size, the DNA of these phages is highly enriched in specific bacterial genes as compared with the bacterial chromosome and may be used as template for in vitro RNA transcription. In order to study the transcription of a bacterial tRNA molecule, we have used the transducing phage φ80psup 3 + (1). The su 3 + gene carried by the φ80 phage is the structural gene which specifies a tRNATyr molecule that enables the amber codon, UAG, to be read as tyrosine (2,3). There are two types of tyrosine tRNA’s (I and II) in E.coli, differing by two nucleotides in the variable loop. The main species in E.coli cells is tRNATyr II; the minor species tRNATyr is specified by two identical genes, one of which can undergo a mutation resulting in a single base change in the anticodon region of the tRNA (su 3 + ). The two tRNATyr I genes are located near the φ80 attachment site on the bacterial chromosome and can be transduced by the φ80 bacteriophage as a single or a tandem double copy.