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D Dash

Publications and source records attributed to D Dash.

22 records · Page 2Linked to original sources
PubMed1985

Interconversion of tight and loose couple 50 S ribosomes and translocation in protein synthesis.

On incubation of 50 S ribosomes, isolated from either tight couple (TC) or loose couple (LC) 70 S ribosomes, with elongation factor G (EG-G) and guanosine 5'-triphosphate, a mixture of TC and LC 50 S ribosomes is formed. There is almost complete conversion of LC 50 S ribosomes to TC 50 S ribosomes on treatment with EF-G, GTP, and fusidic acid. Similarly, TC 50 S ribosomes are converted to LC 50 S ribosomes, although partially, by treatment with EF-G and a GTP analogue like guanyl-5'-yl methylenediphosphate (GMP-P(CH2)P) or guanyl-5'-yl imidodiphosphate (GMP-P(NH)P) and including a polymer of 5'-uridylic acid (poly(U] in the incubation mixture. Furthermore, LC 23 S RNA isolated from LC 50 S ribosomes is converted to TC 23 S RNA on heat treatment, but similar treatment does not affect TC 23 S RNA. The interconversion was followed by several physical and biological characteristics of TC and LC 50 S ribosomes, like association capacities with 30 S ribosomes before and after kethoxal treatment, susceptibility to RNase I and polyphenylalanine-synthesizing capacity in association with 30 S ribosomes, as well as thermal denaturation profiles, circular dichroic spectra, and association capacity of isolated 23 S RNAs. These data strongly support the proposition that TC and LC 50 S ribosomes are the products of translocation during protein synthesis. The conformational change of 23 S RNA induced by EF-G and GTP is most probably responsible for the interconversion, and L7/L12 proteins play an important role in the process. A two-site model based on kethoxal data has also been proposed to explain the tightness and looseness of 70 S couples.

Cell Fractionation↗
PubMed1984

Differences in physical and biological properties of 50S ribosomes and 23S RNAs derived from tight and loose couple 70S ribosomes.

Tight couple (TC) 50S ribosomes on treatment with kethoxal lose their capacity to associate with 30S ribosomes whereas loose couple (LC) 50S ribosomes on such treatment fully retain their association capacity. The same is true for 23S RNAs isolated from treated 50S ribosomes or isolated 23S RNAs directly treated with kethoxal, so far as their capacity to associate with 16S RNA is concerned. At certain Mg++ concentrations TC 23S RNA is highly susceptible to the nucleolytic action of single-strand specific enzyme RNase I; LC 23S RNA is quite resistant. The Mg++-dependencies of the two species of 23S RNAs for association with 16S RNA are also quite different. The fluorescence enhancement of ethidium bromide due to binding to TC 23S RNA is slightly less than LC 23S RNA. The hyperchromicity of LC 23S RNA due to thermal denaturation is somewhat more than TC 23S RNA. LC 23S RNA has slightly more elliptic CD spectrum than TC 23S RNA. These results clearly show that 23S RNAs present in TC and LC 50S ribosomes are distinct from each other. It has been recently demonstrated in this laboratory that they can be interconverted by the agents involved in translocation and thus appear to be conformomers.

Aldehydes↗