Role of adenine functional groups in the recognition of the 3′-splice-site AG during the second step of pre-mRNA splicing

The AG dinucleotide at the 3′ splice sites of metazoan nuclear pre-mRNAs plays a critical role in catalytic step II of the splicing reaction. Previous studies have shown that replacement of the guanine by adenine in the AG (AG → GG) inhibits this step. We find that the second step was even more severely inhibited by cytosine (AG → CG) or uracil (AG → UG) substitutions at this position. By contrast, a relatively moderate inhibition was observed with a hypoxanthine substitution (AG → HG). When adenine was replaced by a purine base (AG → PG) or by 7-deazaadenine (AG → c7AG), little effect on the second step was observed, suggesting that the 6-NH2 and N7 groups do not play a critical role in adenine recognition. Finally, replacement of adenine by 2-aminopurine (AG → 2-APG) had no effect on the second step. Taken together, our results suggest that the N1 group of adenine functions as an essential determinant in adenine recognition during the second step of pre-mRNA splicing.

Differences in antigen recognition and cytolytic activity of CD8+ and CD8− T cells that express the same antigen-specific receptor

CD8+ and CD8− T cell lines expressing the same antigen-specific receptor [the 2C T cell receptor (TCR)] were compared for ability to bind soluble peptide-MHC and to lyse target cells. The 2C TCR on CD8− cells bound a syngeneic MHC (Kb+)-peptide complex 10–100 times less well than the same TCR on CD8+ cells, and the CD8− 2C cells lysed target cells presenting this complex very poorly. Surprisingly, however, the CD8− cells differed little from CD8+ cells in ability to bind an allogeneic MHC (Ld+)-peptide complex and to lyse target cells presenting this complex. The CD8+/CD8− difference provided an opportunity to estimate how long TCR engagements with peptide-MHC have to persist to initiate the cytolytic T cell response.

Heterogeneity in molecular recognition by restriction endonucleases: osmotic and hydrostatic pressure effects on BamHI, Pvu II, and EcoRV specificity.

The cleavage specificity of the Pvu II and BamHI restriction endonucleases is found to be dramatically reduced at elevated osmotic pressure. Relaxation in specificity of these otherwise highly accurate and specific enzymes, previously termed "star activity," is uniquely correlated with osmotic pressure between 0 and 100 atmospheres. No other colligative solvent property exhibits a uniform correlation with star activity for all of the compounds tested. Application of hydrostatic pressure counteracts the effects of osmotic pressure and restores the natural selectivity of the enzymes for their canonical recognition sequences. These results indicate that water solvation plays an important role in the site-specific recognition of DNA by many restriction enzymes. Osmotic pressure did not induce an analogous effect on the specificity of the EcoRV endonuclease, implying that selective hydration effects do not participate in DNA recognition in this system. Hydrostatic pressure was found to have little effect on the star activity induced by changes in ionic strength, pH, or divalent cation, suggesting that distinct mechanisms may exist for these observed alterations in specificity. Recent evidence has indicated that BamHI and EcoRI share similar structural motifs, while Pvu II and EcoRV belong to a different structural family. Evidently, the use of hydration water to assist in site-specific recognition is a motif neither limited to nor defined by structural families.

Trades unionism and its results. Five letters in 'The Times'; with some additions.

Cover-title.

Citizens of long ago; essays on life and letters in the Roman Empire,

Introduction signed: Grant Showerman.

Memoirs of a Magdalen or The history of Louisa Mildway : now first published from a series of original letters, in two volumes ; vol.I [-II]

Mode of access: Internet.

Proofs of the interpolation of the vowel-letters in the text of the Hebrew Bible and grounds thence derived for a revision of its authorized English version /

Errata slip inserted.

Lincoln's imagery, a study in word power.

Bibliographical footnotes.

A collection of all the humorous letters in the London journal.

Signatures: A-H⁴.

Three essays : On the intermediate state of the dead; The resurrection from the dead; and On the Greek terms rendered judge, judgment, condemned, condemnation, damned, damnation, etc. in the New Testament; with remarks on Mr. Hudson's letters in vindication of a future retribution, addressed to Mr. Hosea Ballou /

Mode of access: Internet.

Otis' letters in defence of the Hartford Convention, and the people of Massachusetts.

Cover title.

An antidote against deism : in a series of letters ... in which the arguments against the eternal prevalence of sin and misery and in favor of the restitution or final restoration of all things are candidly stated from Scripture and also an answer to objections; ... to which are added a review of President Edwards̓ sermon on the eternity of hell torments ... also some strictures on Dr. Rylands̓ sermon entitled The first lie refuted /

Page 267 incorrectly numbered 297.