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The B-cell mitogens lipopolysaccharide (LPS), Nocardia water-soluble mitogen (NWSM), and dextran sulfate (DxS) react with different subpopulations of B lymphocytes. Selective in vitro killing of cells responding to either LPS or NWSM has little effect on the in vitro response to the other mitogen, although the response to DxS is reduced in both cases. If, after selective in vitro killing, cells are injected into irradiated mice for 2-3 wk before measuring their in vitro mitogen responses, the same specificity pattern is seen. Thus, one is dealing with different B-cell subpopulations rather than different stages of maturation of a single population. Treatment with various alloantisera and complement before measuring the mitogen response to LPS and NWSM shows that (a) whereas all LPS response cells carry surface Ig, a subpopulation of NWSM responsive cells does not; (b) both LPS- and NWSM-responsive cells carry I-A antigens but might not I-E or I-J antigens; (c) all LPS-responsive cells carry I-C antigens, whereas approximately 25% of NWSM responsive cells do not: (d) there is a subpopulation of NWSM-responsive cells carrying neither surface Ig nor I-C antigens and resistant to anti-theta treatment.

Ia antigens from the I-A8 and I-Ck subregions of the B10.HTT (H-2t3) strain of mice were isolated by indirect immunoprecipitation of arginine-labeled, nonionic detergent-solubilized materials. After biochemical purification the electrophoretically homogeneous 28,000 dalton glycoprotein beta chains from the Ia precipitates were digested with trypsin and the resultant radiolabeled tryptic peptides were compared by analytical ion exchange chromatography. These comparisons reveal that the beta chains of Ia antigens from the A (I-A8) and C (I-Ck) subregions of B10.HTT share only two out of 12 to 14 of their arginine tryptic peptides. Thus these noncross-reactive Ia antigens are structurally quite diverse, and would possess sufficient structural variability to account for their lack of antigenic cross-reactivity.

Summary Oligonucleotides corresponding to the E. coli tRNA fMet have been synthesized. A diester approach has been used for the synthesis of 6 , 7 , 8 and 9 . A block condensation of nucleotides with 3′-phosphodiesters has been applied to the synthesis of 2 , 3 , 4 and 5 . A new phosphorylating reagent, p-chlorophenyl N-phenylphosphoroamido chloride was synthesized and used for this purpose. Joining of previously synthesized fragments with T4 RNA ligase yielded an eicosanucleotide ( 1 + 2 ) corresponding to bases 1–20 from the 5′-end.