Cell stress, viral infection, and translational inhibition increase the abundance of human Alu RNA, suggesting that the level of these transcripts is sensitive to the translational state of the cell. To determine whether Alu RNA functions in translational homeostasis, we investigated its role in the regulation of double-stranded RNA-activated kinase PKR. We found that overexpression of Alu RNA by cotransient transfection increased the expression of a reporter construct, which is consistent with an inhibitory effect on PKR. Alu RNA formed stable, discrete complexes with PKR in vitro, bound PKR in vivo, and antagonized PKR activation both in vitro and in vivo. Alu RNAs produced by either overexpression or exposure of cells to heat shock bound PKR, whereas transiently overexpressed Alu RNA antagonized virus-induced activation of PKR in vivo. Cycloheximide treatment of cells decreased PKR activity, coincident with an increase in Alu RNA. These observations suggest that the increased levels of Alu RNAs caused by cellular exposure to different stresses regulate protein synthesis by antagonizing PKR activation. This provides a functional role for mammalian short interspersed elements, prototypical junk DNA.

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Four consecutive T residues in the sense strand are sufficient to terminate transcription by RNA polymerase III (pol III). Previously we observed that compared with this minimally sufficient terminator, five T residues immediately preceded by a palindromic sequence increases transcriptional expression both in vitro and in vivo, raising the question of whether a palindromic sequence has a role in pol III termination. Here we observe that site-directed mutations which eliminate the dyad symmetry of the palindromic sequence decrease transcriptional expression. Similar effects are observed whether dyad symmetry is eliminated in regions of the palindrome which are proximal or distal with respect to the terminator. Compensatory mutations at either site to restore dyad symmetry rescue transcriptional activity. These observations suggest that a higher order structure, such as a RNA hairpin, immediately preceding the terminator increases pol III transcriptional activity.

Identifiler-Employees and students of Muhimibili University College of Health Sciences in Dar es Salaam representing 19 widely distributed administrative districts and 42 tribes within the country.