[Frontiers in Bioscience 3, d1241-1252, December 1, 1998]

	[Frontiers in Bioscience 3, d1241-1252, December 1, 1998] Reprints PubMed CAVEAT LECTOR
	INHIBITION OF INTERNAL ENTRY SITE (IRES)-MEDIATED TRANSLATION BY A SMALL YEAST RNA: A NOVEL STRATEGY TO BLOCK HEPATITIS C VIRUS PROTEIN SYNTHESIS Saumitra Das¹, Michael Ott², Akemi Yamane¹, Arun Venkatesan¹, Sanjeev Gupta² and Asim Dasgupta¹ Department of Microbiology, Molecular Genetics and Immunolog, UCLA School of Medicine, 10833 Le Conte Avenue, Los Angeles, CA 90095-1747¹, ²Department of Medicine, Albert Einstein, College of Medicine of Yeshiva University, Bronx, New York 10461-1602 Received 9/18/98 Accepted 9/23/98 4. STRUCTURE OF IRNA 4.1. Structure of I-RNA is important for the inhibitory activity Since both the picornaviral 5´ -UTR and I-RNA bind similar proteins involved in internal initiation of translation, the obvious question is whether there is any sequence homology between these RNAs. We found no significant homology of I-RNA with any picornaviral RNA. Furthermore, the antisense I-RNA (complementary sequence of I-RNA) was found to be almost equally active in blocking IRES-mediated translation (Venkatesan, Das and Dasgupta, unpublished). Taken together, it is plausible that I-RNA might fold into a secondary structure that could be very similar to a portion of the IRES element of the picornaviral RNAs. In fact, the secondary structure predicted by the Zuker MFOLD modeling program shows that a stem loop formed by intramolecular folding of I-RNA resembles the conserved core structure of the picornavirus IRES element (Ref. 54 and unpublished results) (figure 6). Thus it appears that the structure rather than the primary sequence of I-RNA molecule is the major determinant for selective inhibition of IRES mediated translation. Figure 6. Predicted secondary structures of IRNA. Two computer predicted secondary structures of IRNA are shown. Recent results show that the form depicted in (A) is the actual secondary structure of IRNA. 4.2. I-RNA encoding gene in Saccharomyces Cerevisiae Sequence analysis of the region spanning the active site of I-RNA (at 16-60) have been found to be highly homologous to an yeast chromosome 3 fragment while the leader sequence (nt 1-15) may be encoded by a chromosome 12 fragment. It is possible that the I-RNA encoding gene originates from two different chromosomes, however since IRNA was originally isolated from the ABYS1 strain of S. cerevisiae, further experimentation is necessary to understand whether this discontinuity in sequence is due to trans splicing or simply reflects a strain variation between ABYS1 and the data base strain.

[Frontiers in Bioscience 3, d1241-1252, December 1, 1998]
Reprints
PubMed
CAVEAT LECTOR

INHIBITION OF INTERNAL ENTRY SITE (IRES)-MEDIATED TRANSLATION BY A SMALL YEAST RNA: A NOVEL STRATEGY TO BLOCK HEPATITIS C VIRUS PROTEIN SYNTHESIS

Saumitra Das¹, Michael Ott², Akemi Yamane¹, Arun Venkatesan¹, Sanjeev Gupta² and Asim Dasgupta¹

Department of Microbiology, Molecular Genetics and Immunolog, UCLA School of Medicine, 10833 Le Conte Avenue, Los Angeles, CA 90095-1747¹, ²Department of Medicine, Albert Einstein, College of Medicine of Yeshiva University, Bronx, New York 10461-1602

Received 9/18/98 Accepted 9/23/98

4. STRUCTURE OF IRNA

4.1. Structure of I-RNA is important for the inhibitory activity

Since both the picornaviral 5´ -UTR and I-RNA bind similar proteins involved in internal initiation of translation, the obvious question is whether there is any sequence homology between these RNAs. We found no significant homology of I-RNA with any picornaviral RNA. Furthermore, the antisense I-RNA (complementary sequence of I-RNA) was found to be almost equally active in blocking IRES-mediated translation (Venkatesan, Das and Dasgupta, unpublished). Taken together, it is plausible that I-RNA might fold into a secondary structure that could be very similar to a portion of the IRES element of the picornaviral RNAs. In fact, the secondary structure predicted by the Zuker MFOLD modeling program shows that a stem loop formed by intramolecular folding of I-RNA resembles the conserved core structure of the picornavirus IRES element (Ref. 54 and unpublished results) (figure 6). Thus it appears that the structure rather than the primary sequence of I-RNA molecule is the major determinant for selective inhibition of IRES mediated translation.

Figure 6. Predicted secondary structures of IRNA. Two computer predicted secondary structures of IRNA are shown. Recent results show that the form depicted in (A) is the actual secondary structure of IRNA.

4.2. I-RNA encoding gene in Saccharomyces Cerevisiae

Sequence analysis of the region spanning the active site of I-RNA (at 16-60) have been found to be highly homologous to an yeast chromosome 3 fragment while the leader sequence (nt 1-15) may be encoded by a chromosome 12 fragment. It is possible that the I-RNA encoding gene originates from two different chromosomes, however since IRNA was originally isolated from the ABYS1 strain of S. cerevisiae, further experimentation is necessary to understand whether this discontinuity in sequence is due to trans splicing or simply reflects a strain variation between ABYS1 and the data base strain.