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Abstract: Ribosomal protein S20 is a primary binding protein that bridges the 5′ domain and the 3′ minor domain of the 16S ribosomal RNA (rRNA) in the 30S ribosomal subunit. Using time-dependent dimethyl sulfate modification, we have determined that as it is bound to 16S rRNA, protein S20 causes rapid protection of bases A246, A274, A279, and A282 in the stem region of helix 11 in the 5′ domain and moderately fast modifications of helix 44 bases A1433 and A1434 in the 3′ minor domain. At a later time, enhancements occur with bases A181and A190 in helix 9, bases A325 and A327 in helix 13, and base C264 at the distal end of helix 11 in the 5′ domain of 16S rRNA. The modifications that occur in the stem region of helix 11 are distant from the binding site of protein S20, as determined from the crystal structure. Simultaneous addition of protein S17 with S20 to the complex significantly alters the modifications caused by protein S20 in the stem region of helix 11 but does not alter the remaining modifications. Our results indicate that protein S20 is binding to at least two alternate 16S rRNA sites during the early assembly process. [ABSTRACT FROM AUTHOR]

Abstract: Ribosomal subunit assembly is initiated by the binding of several primary binding proteins. Results from chemical modification studies show that 16S ribosomal RNA undergoes striking structural rearrangements when protein S17 is bound. For the first time, we are able to distinguish and order these structural rearrangements by using time-dependent chemical probing. Initially, protein S17 binds to a portion of helix 11, inducing a kink-turn in that helix that bends helix 7 toward the S17–helix 11 complex in a hairpin-like manner, allowing helix 7 to bind to protein S17. This structural change is rapidly stabilized by interactions at the distal and proximal ends of both RNA helices. Identifying the dynamic nature of interactions between RNA and proteins is not only essential in unraveling ribosome assembly, but also has more general application to all protein–RNA interactions. [Copyright &y& Elsevier]

This paper provides information concerning the flexibility of leader behavior. Subjects were 48 black and 48 white undergraduate students. Twelve black and 12 white older students were selected as leaders while the remaining subjects were assigned randomly as members of 12 black, 12 white, and 12 mixed dyads. Results indicate that leader behavior as measured by Bales Interaction Process Analysis changed as the group performed different tasks. There were no behavior differences as a function of leader's race although an interaction was found in the directive categories between task and dyad composition. [ABSTRACT FROM AUTHOR]

This paper measured subordinates' perceptions of their leaders' ability to use different leadership styles. Subjects were 124 middle and first level supervisors from accounting and R & D departments in the United Kingdom. The results indicate that subjects did not believe that their supervisors would either use the same style (irrespective of what style) or randomly employ styles to deal with four typical but hypothetical problems. These results persisted when respondents were subdivided on the basis of both organizational level and functional area. Some evidence suggests that perceived patterns of style usage may be associated, at least in the mind of subordinates, with the general task dimension, interpersonal-technical. [ABSTRACT FROM AUTHOR]

Abstract: The penultimate stem–loop of 16S ribosomal RNA (rRNA), helix 44, plays a central role in ribosome function. Using time-resolved dimethyl sulfate (DMS) probing, we have analyzed time-dependent modifications that occur at specific bases in this helix near the decoding region, resulting from the binding of elongation factor G (EF-G) in various forms. When EF-G-GTP is bound to 70S ribosomes, bases A1492 and A1493 are immediately protected, while other bases in the region show either no change or enhanced modification. When apo-EF-G is bound to 70S ribosomes and GTP is added, substantial transient time-dependent enhancement occurs at bases A1492 and A1493, with somewhat less enhancement occurring at base A1483, all in the first 45 ms. When mRNA and deacylated tRNAs are bound to the 70S ribosome and EF-G-GTP is added, bases A1492 and A1493 again show substantial and continued enhancement, while bases A1408, A1413, and A1418 all show time-dependent protection. These results provide primary, real-time evidence that EF-G induces direct or indirect structural changes in this region as EF-G is bound and as GTP is hydrolyzed. [Copyright &y& Elsevier]

Abstract: Time-dependent chemical modification and cleavage results have provided intriguing insights into structural changes that occur in the distal loop of helix 11 in 16S ribosomal RNA (rRNA). Located distant from the decoding region, between proteins S17 and S20, the results of this study suggest that this region of rRNA may act as a buffer or a spring between these two proteins during protein biosynthesis. During the assembly process, protein S17 apparently produces the major structural deformations in this region, causing it to be folded in a spring-like structure. Base C264 in this region shows erratic behavior during assembly and also shows time-dependent enhancement when elongation factor G with GTP is added to 70S ribosomes. Evidence is presented to suggest that this region of rRNA may be used to allow relative motion to occur between proteins S17 and S20 during translocation. [Copyright &y& Elsevier]

The notion that the ribosome is dynamic has been supported by various biochemical techniques, as well as by differences observed in high-resolution structures of ribosomal complexes frozen in various functional states. Yet, the mechanisms and extent of rRNA dynamics are still largely unknown. We have used a novel, fast chemical-modification technique to provide time-resolved details of 16S rRNA structural changes that occur as bridges are formed between the ribosomal subunits as they associate. Association of different 16S rRNA regions was found to be a sequential, multi-step process involving conformational rearrangements within the 30S subunit. Our results suggest that key regions of 16S rRNA, necessary for decoding and tRNA A-site binding, are structurally altered in a time-dependent manner by association with the 50S ribosomal subunits. [Copyright &y& Elsevier]

Bacterial translation initiation factor IF2 was localized on the ribosome by rRNA cleavage using free Cu(II):1,10-orthophenanthroline. The results indicated proximity of IF2 to helix 89, to the sarcin–ricin loop and to helices 43 and 44, which constitute the “L11/thiostrepton” stem-loops of 23 S rRNA. These findings prompted an investigation of the L11 contribution to IF2 activity and a re-examination of the controversial issue of the effect on IF2 functions of thiostrepton, a peptide antibiotic known primarily as a powerful inhibitor of translocation. Ribosomes lacking L11 were found to have wild-type capacity to bind IF2 but a strongly reduced ability to elicit its GTPase activity. We found that thiostrepton caused a faster recycling of this factor on and off the 70 S ribosomes and 50 S subunits, which in turn resulted in an increased rate of the multiple turnover IF2-dependent GTPase. Although thiostrepton did not inhibit the P-site binding of fMet-tRNA, the A-site binding of the EF-Tu-GTP-Phe-tRNA or the activity of the ribosomal peptidyl transferase center (as measured by the formation of fMet-puromycin), it severely inhibited IF2-dependent initiation dipeptide formation. This inhibition can probably be traced back to a thiostrepton-induced distortion of the ribosomal-binding site of IF2, which leads to a non-productive interaction between the ribosome and the aminoacyl-tRNA substrates of the peptidyl transferase reaction. Overall, our data indicate that the translation initiation function of IF2 is as sensitive as the translocation function of EF-G to thiostrepton inhibition. [Copyright &y& Elsevier]