Human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) initiates DNA synthesis from the 3' end of human tRNA(Lys3). We have used cis-acting hammerhead ribozymes to produce homogeneous-length transcribed tRNA(Lys3) and have developed conditions for purifying highly structured RNAs on a modified tube-gel apparatus. Titration experiments show that this RNA can assemble into an initiation complex that contains equimolar amounts of HIV-1 RT, transcribed tRNA(Lys3), and chemically synthesized template RNA. We have purified this complex using gel-filtration chromatography and have found that it is homogeneous with respect to molecular weight, demonstrating that the initiation complex forms a single discrete species at micromolar concentrations. When this initiation complex is supplied with deoxynucleotides, essentially all of the tRNA is used as a primer by HIV-1 RT and is fully extended to the 5' end of the template. Thus, in vitro transcribed tRNA can be used efficiently as a primer by HIV-1 RT. We have also obtained crystals of the HIV-1 initiation complex that require the precisely defined ends of this in vitro transcribed tRNA(Lys3) to grow.

The relationship between the synthesis and methylation of nucleic acids in tissue slices from higher plant storage organs has been investigated. Although the observed nucleic acid synthesis is mainly an expression of rRNA synthesis the highest level of methylation occurs in tRNA. Unlike the synthesis and methylation of rRNA which appears completely coupled, the methylation of tRNA is not tightly coupled to its synthesis. It is suggested that a pool of undermethylated tRNA exists in the tissue prior to incubation and that methylation of this tRNA initially controls the rate of protein synthesis in the tissue slices.

The effects of various inhibitors of protein and nucleic acid synthesis on the development of invertase activity and increased nucleolar volume in discs excised from tubers of artichoke tissue are compared. The results are discussed with reference to the current theories relevant to the action of the inhibitors and to the nature of the increase in nucleolar volume.

Some of the possible uses of tissue slices derived from the storage organs of higher plants are described. During the incubation of tissue slices in distilled water, fundamental and rapid changes occur. The changes are thought to be part of a new develop mental sequence initiated by excision. The processes underlying these changes are seen to operate in other more complex systems. Experiments are described in which inhibitors are used to investigate the timing of transcription and translation of the messenger RNA for the enzyme invertase. It is suggested that plant tissue slices provide adaptable material with which to study enzyme induction, protein synthesis, and cell differentiation at sixth-form level.