Front Cover; Progress in Nucleic Acid Research and Molecular Biology, Volume 32; Copyright Page; Contents; Contributors; Abbreviations and Symbols; Some Articles Planned for Future Volumes; Chapter 1. Gene Conversion in Trypanosome Antigenic Variation; I. Summary; ll. Antigenic Variation Is due to Differential Gene Expression; lll. Antigen Gene Expression Is Often Linked to DNA Rearrangements; IV. Evidence for Gene Conversion as a Mechanism for Antigenic Variation; V. The Extent of Gene Conversion Is Variable, Depending on the Degree of Homology between the Recombinant Sequences.

VI. Gene Conversion EndpointsVlI. Gene Conversion Frequency; VIII. Orientation of the Gene Conversion Mechanism; Relationship with Transcription; IX. Gene Conversion and Antigen Repertoire Evolution; X. Sexual Conjugation Further Leads to Evolution of the Antigen Gene Repertoire; XI. Problems and Outlooks; References; Chapter 2. Hypermodified Nucleosides of tRNA: Synthesis, Chemistry, and Structural Features of Biological Interest; I. Hypermodified Nucleosides of tRNA: A Bioorganic Chemist's View; ll. Synthesis and Chemistry.

Lll. Structural Features of Hypermodified Nucleosides and Codon-Anticodon InteractionReferences; Chapter 3. Ribosomal Translocation: Facts and Models; I. Definition; ll. Experimental Tests; Ill. Two-tRNA-Site Model for the Ribosomal Elongation Cycle; IV. Main Facts Concerning Translocation; V. Sequence of Events in Translocation Promoted by EF-G; VI. Energetics of Translocation; VII. Kinematics of Translocation; VIII. Are Conformational Movements of the Ribosome Required for Translocation?; IX. Concluding Remarks; References; Chapter 4. Chemical Changes Induced in DNA by Ionizing Radiation.

I. The Mechanisms by which Ionizing Radiations Act on DNAIl. Indirect Action: The Effects of Reactive Species Formed from Water on DNA in Dilute Solution; lll. Effects of Irradiation in the SoIid State; IV. Irradiation of DNA in Cells; V. Quantitative Measurements That Should Be Made on Irradiated DNA; References; Chapter 5. Comparative Anatomy of 16-S-like Ribosomal RNA; I. Comparative Anatomy of 16-S-like Ribosomal RNA; Il. A Computer-Assisted Search for Coordinated Base Changes in 16-S rRNA; References; Chapter 6. SV40 Promoters and Their Regulation; I. Regulatory Region of SV40.

Il. DNA Binding Property of T Antigenlll. Regulation of Transcription; IV. Conclusions; References; Chapter 7. The Role of the Anticodon in Regulation of tRNA by Aminoacyl-tRNA Synthetases; I. Concise Background of the Problem; ll. The Role of the Anticodon in Acceptor Function; lll. General Remarks; References; Chapter 8. Properties and Spatial Arrangement of Components in Preinitiation Complexes of Eukaryotic Protein Synthesis; I. Arrangement of Proteins in Small Ribosomal Subunits; ll. Function and Arrangement of Components in Preinitiation Complexes; lll. Summary and Conclusions.