Kazumi Hosono

A single uridine modification at the wobble position of an artificial tRNA enhances wobbling in an Escherichia coli cell-free translation system

5‐Methoxyuridine was introduced into the first position of the anticodon of the unmodified form of tRNA1 Ser from Escherichia coli. The codon reading efficiencies of this tRNA (tRNA(5‐methoxyuridine UGA)) relative to those of the unmodified counterpart (tRNA(UGA)) were measured in a cell‐free translation system. tRNA(5‐methoxyuridine UGA) was more efficient than tRNA(UGA) in the reading of the UCU and UCG codons and was less efficient in the reading of the UCA codon. Thus, the single modification of U to 5‐methoxyuridine can enhance the wobble readings.

Properties and Anti-HIV Activity of Nicked Dumbbell Oligonucleotides

Abstract We have designed a new type of oligodeoxyribonucleotide. These oligodeoxyribonucleotides form two hairpin loop structures with base pairs (sense and antisense) in the double helical stem at the 3′ and 5′-ends (nicked dumbbell oligonucleotides). The nicked dumbbell oligonucleotides are molecules with free ends that are more resistant to exonuclease attack. Furthermore, the nicked dumbbell oligonucleotide containing phosphorothioate (P=S) bonds in the hairpin loops has increased nuclease resistance, as compared to the unmodified nicked oligonucleotide. The binding of the nicked dumbbell oligonucleotide to RNA is lower than that of a single-stranded DNA. We also describe the anti-HIV activity of nicked dumbbell oligonucleotides. #This article is dedicated to Professor Yoshihisa Mimno on the occasion of his 75 th birthday.

Properties and Anti-Hiv Activity of Hairpin Antisense Oligonucleotides Containing 2′-Methoxynucleosides with Base-Pairing in the Stem Region at the 3′-End

A new type of hairpin antisense oligodeoxyribo-nucleotide, containing 2′-methoxynucleosides with base-pairing in the stem region at the 3′-end, was tested for 3′-exonuclease resistance and anti-HIV activity. An increased resistance to nuclease degradation has been observed by incubation of the hairpin oligo-nucleotides with DNA polymerase and foetal bovine serum. Of particular interest is the hairpin antisense oligonucleotide containing 2′-methoxynucleosides with base-pairing in the stem region at the 3′-end, which has increased nuclease resistance and hybridizes effectively with a complementary RNA. Furthermore, these compounds were assayed for inhibition of virus replication in HIV-1 infected MT-4 cells. In the anti-HIV activity test, the hairpin oligonucleotide phosphorothioate derivatives showed higher anti-HIV activities compared to their linear counterparts.

Self-cleavage of p2Sp1 RNA with Mg2+ and non-ionic detergent (Brij 58).

The precursor of an RNA molecule from T4-infected E. coli cells (p2Sp1 RNA) has the capacity to cleave itself at specific positions [(UpA (139-140) and CpA (170-171)], within a putative loop and stem structure. This sequence-specific cleavage requires at least a monovalent cation and non-ionic detergents. We studied the self-cleavage reaction of an RNA fragment (GUUUCGUACAAAC) (R1) with the sequence corresponding to the p2Sp1 RNA in the presence of Mg2+ and non-ionic detergents. It requires Mg2+ and is aided by a non-ionic detergent, Brij 58. The cleavage reaction is time, temperature, and pH-dependent. The cleavage occurs at the phosphodiester bond between UpA and CpA on the RNA fragment (GUUUCGUACAAAC) (R1). Furthermore, the maximum of cleavage of R1 occurs at a very low Mg2+ concentration (< or = 5 mM).

The stem hairpin loop structure of p2Sp1 RNA is required for RNA-cleaving activity

We studied the hairpin-loop structure of an RNA fragment (GUUUCGUACAAAC) (R13) with the sequence corresponding to the self-cleavage domain in the precursor of an RNA molecule from bacteriophage T4-infected Escherichia coli cells (p2Sp1 RNA). In order to determine the influence of the hairpin-loop structure on these sequence-specific cleavage reactions, we have synthesized oligoribonucleotides containing hairpin-loop, double-helical stem-loop, and single-stranded RNA structures. The cleavage was affected by the hairpin-loop structure. Furthermore, the helix-stem, which retains the thermodynamically extrastable stem hairpin-loop structures, is also important for the cleavage activity. However, the thermodynamically extrastable helix-stem structure reduced the cleavage activity of the adjacent UA and CA sequences at the helix-stem site. For the cleavage reactions of the RNA cleavage products, the R6 (ACAAAC), R7 (GUUUCGU), and R9 (GUUUCGUAC) mers from the parent RNA, R13 (GUUUCGUACAAAC), a very slight amount of cleavage product (2%) from the RNA 9 was observed, but no reaction occurred for the R6 and R7. We also describe the influences of the sequences (UA and CA) on the cleavage activity.