An in vivo approach to tRNA identity

A leucine-inserting tRNA has been transformed into a serine-inserting tRNA by changing 12 nucleotides. Only 8 of the 12 changes are required to effect the conversion of the leucine tRNA to serine tRNA identity. The 8 essential changes reside in basepair 11-24 in the D stem, basepairs 3-70, 2-71 and nucleotides 72 and 73, all of the acceptor stem.

Functional amber suppressor tRNA genes were generated for 14 species of tRNA in E. coli, and their amino acid specificities determined. The suppressors can be classified into three groups, based upon their specificities. Class I suppressors, tRNA^(Ala2)_(CUA), tRNA^(GlyU)_(CUA), tRNA^(HisA)_(CUA), tRNA^(Lys)_(CUA), and tRNA^(ProH)_(CUA), inserted the predicted amino acid. The Class II suppressors, tRNA^(GluA)_(CUA) , tRNA^(GlyT)_(CUA), and tRNA^(Ile1)_(CUA) were either partially or predominantly mischarged by the glutamine aminoacyl tRNA synthetase (AAS). The Class III suppressors, tRNA^(Arg)_(CUA), tRNA^(AspM)_(CUA), tRNA^(Ile2)_(CUA), tRNA^(Thr2)_(CUA), tRNA^(Met(m))_(CUA) and tRNA^(Val)_(CUA) inserted predominantly lysine.

On an embedding property of generalized Carter subgroups

If <i>Ei> and <i>Fi> are saturated formations, we say that <i>Ei> is strongly contained in <i>Fi> if for any solvable group G with <i>Ei>-subgroup, E, and <i>Fi>-subgroup, F, some conjugate of E is contained in F. In this paper, we investigate the problem of finding the formations which strongly contain a fixed saturated formation <i>Ei>.

Our main results are restricted to formations, <i>Ei>, such that <i>Ei> = {G|G/F(G) ϵ<i>Ti>}, where <i>Ti> is a non-empty formation of solvable groups, and F(G) is the Fitting subgroup of G. If <i>Ti> consists only of the identity, then <i>Ei>=<i>Ni>, the class of nilpotent groups, and for any solvable group, G, the <i>Ni>-subgroups of G are the Carter subgroups of G.

We give a characterization of strong containment which depends only on the formations <i>Ei>, and <i>Fi>. From this characterization, we prove:

If <i>Ti> is a non-empty formation of solvable groups, <i>Ei> = {G|G/F(G) ϵ<i>Ti>}, and <i>Ei> is strongly contained in <i>Fi>, then

(1) there is a formation <i>Vi> such that <i>Fi> = {G|G/F(G) ϵ<i>Vi>}.

(2) If for each prime p, we assume that <i>Ti> does not contain the class, <i>Si>_p’, of all solvable p’-groups, then either <i>Ei> = <i>Fi>, or <i>Fi> contains all solvable groups.

This solves the problem for the Carter subgroups.

We prove the following result to show that the hypothesis of (2) is not redundant:

If <i>Ri> = {G|G/F(G) ϵ<i>Si>_r’}, then there are infinitely many formations which strongly contain <i>Ri>.