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A novel mutation in ribosomal protein S4 thataffects the function of a mutated RF1
Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
2000 (English)In: Biochimie, ISSN 0300-9084, Vol. 82, no 8, 683-691 p.Article in journal (Refereed) Published
Abstract [en]

Release factors (RF) 1 and 2 trigger the hydrolysis of the peptide from the peptidyl-tRNA during translation termination. RF1 binds to the ribosome in response to the stop codons UAG and UAA, whereas RF2 recognizes UAA and UGA. RF1 and RF2 have been shown to bind to several ribosomal proteins. To study this interaction in vivo, prfA1, a mutant form of RF1 has been used. A strain with the prfA1 mutation is temperature sensitive (Ts) for growth at 42 °C and shows an increased misreading of UAG and UAA. In this work we show that a point mutation in ribosomal protein S4 can, on the one hand, make the RF1 mutant strain Ts+; on the other hand, this mutation increases the misreading of UAG, but not UAA, caused by prfA1. The S4 mutant allele, rpsD101, is a missense mutation (Tyr51 to Asp), which makes the cell cold sensitive. The behaviour of rpsD101 was compared to the well-studied S4 alleles rpsD12, rpsD14, and rpsD16. These three mutations all confer both a Ts (44 °C) phenotype and show a ribosomal ambiguity phenotype, which rpsD101 does not. The three alleles were sequenced and shown to be truncations of the S4 protein. None of the three mutations could compensate for the Ts phenotype caused by the prfA1 mutation. Hence, rpsD101 differs in all studied characteristics from the three above mentioned S4 mutants. Because rpsD101 can compensate for the Ts phenotype caused by prfA1 but enhances the misreading of UAG and not UAA, we suggest that S4 influences the interaction of RF1 with the decoding center of the ribosome and that the Ts phenotype is not a consequence of increased readthrough.

Place, publisher, year, edition, pages
Société de chimie biologique , 2000. Vol. 82, no 8, 683-691 p.
Keyword [en]
RF1; S4; translational termination; readthrough; stop codon
National Category
Biological Sciences
Research subject
Microbiology
Identifiers
URN: urn:nbn:se:su:diva-23269DOI: 10.1016/S0300-9084(00)01160-3OAI: oai:DiVA.org:su-23269DiVA: diva2:191055
Note
Part of urn:nbn:se:su:diva-216Available from: 2004-08-26 Created: 2004-08-26 Last updated: 2010-01-07Bibliographically approved
In thesis
1. Function and regulation of release factor one in Escherichia coli
Open this publication in new window or tab >>Function and regulation of release factor one in Escherichia coli
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During translation termination the stop codons UAA and UAG are recognised by release factor one (RF1). RF1 binds to the ribosome and mediates the hydrolysis of the nascent peptide from the peptidyl-tRNA. In this process, RF1 interacts directly or indirectly with several ribosomal proteins (r-proteins). To study this interaction in vivo we have used a mutant allele of RF1, prfA1. The mutation causes a temperature sensitive (Ts) phenotype and increased readthrough of the stop codons. A mutant form of r-protein S4 that suppresses this Ts phenotype was isolated. The S4 mutant also increases the readtrough of UAG caused by prfA1. In the mutated S4 allele, rpsD101, Tyr51 is changed to Asp. That change introduces a negatively charged amino acid in a part of S4 that belongs to the positively charged RNA binding surface. This might affect the binding of S4 to the 16S rRNA, to another r-protein, or to RF1, and in that way influence on the function of RF1.

One of the few things known about the regulation of RF1 is that expression is decreased with increasing generation time. prfA is the second gene in the hemA-operon located at 27 minutes on the E. coli chromosomal map. We have shown that the growth rate regulation of RF1 is exerted at one of the promoters preceding the hemA gene, PhemA1. The promoter is also growth phase regulated and it is turned off in stationary phase. We have characterised two mutations, asuA1 and asuA2, that increase expression of RF1. The asuA2 mutation is a G to A change one nucleotide downstream of the -10 region of PhemA1. Besides increasing expression of RF1 this mutation also abolishes the growth rate and growth phase regulations we have found. The growth phase regulation is partly dependent on ppGpp. We present two models concerning the effect of ppGpp on PhemA1, and what the asuA2 mutation does to it. The prfA gene has low translation initiation efficiency due to a long spacing between the Shine-Dalgarno (SD) sequence and the start codon. The asuA1 mutation creates a new start codon with a shorter distance to the SD sequence. Most likely this increases the efficiency of translation initiation. That PhemA1 is turned off in stationary phase suggests additional regulation of RF1. Our results indicate a putative promoter for the prfA gene within hemA. This promoter does not seem to be growth rate or growth phase regulated.

Place, publisher, year, edition, pages
Stockholm: Institutionen för genetik, mikrobiologi och toxikologi, 2004. 60 p.
Keyword
molekylärgenetik
National Category
Microbiology
Identifiers
urn:nbn:se:su:diva-216 (URN)91-7265-919-X (ISBN)
Public defence
2004-09-16, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-08-26 Created: 2004-08-26Bibliographically approved

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