A genomic clone that specifies a single polypeptide precursor for ricin, a toxic lectin of Ricinus communis (castor bean), was isolated, sequenced and Sl mapped. The gene encodes a 64 kDa precursor which contains, in the following order: a 24 or 35 amino acid signal peptide, the A chain, a 12 amino acid linker peptide, and the B chain. The 5'-end of the ricin mRNA maps approximately 35 bases upstream from the first methionine codon. Two putative TATA boxes and a possible CAAT box lie in the 5'-flanking region. Two possible polyadenylation signals were found in the 3' flanking region. No introns were found, which is typical of other lectin genes that have been sequenced. Southern blot analysis suggests that the castor bean genome contains approximately six ricin-like genes.

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Cloned DNAs encoding four different proteins have been isolated from recombinant cDNA libraries constructed with Glycine max seed mRNAs. Two cloned DNAs code for the alpha and alpha'-subunits of the 7S seed storage protein (conglycinin). The other cloned cDNAs code for proteins which are synthesized in vitro as 68,000 d., 60,000 d. or 53,000 d. polypeptides. Hybrid selection experiments indicate that, under low stringency hybridization conditions, all four cDNAs hybridize with mRNAs for the alpha and alpha'-subunits and the 68,000 d., 60,000 d. and 53,000 d. in vitro translation products. Within three of the mRNA, there is a conserved sequence of 155 nucleotides which is responsible for this hybridization. The conserved nucleotides in the alpha and alpha'-subunit cDNAs and the 68,000 d. polypeptide cDNAs span both coding and noncoding sequences. The differences in the coding nucleotides outside the conserved region are extensive. This suggests that selective pressure to maintain the 155 conserved nucleotides has been influenced by the structure of the seed mRNA. RNA blot hybridizations demonstrate that mRNA encoding the other major subunit (beta) of the 7S seed storage protein also shares sequence homology with the conserved 155 nucleotide sequence of the alpha and alpha'-subunit mRNAs, but not with other coding sequences.

Analysis of the expression of genes encoding the f-conglycinin seed storage proteins in soybean has been used to extend our understanding of developmental gene expression in plants. The a, a', and ,B subunits of S-conglycinin are encoded by a multigene family which is organ-specific in its expression. In this study we report the differentially proammed accumulation of the a, a', and h subunits of ,B-conglycinin. Multiple isomeric forms of each subunit are present in the dry seed, but the timing of their accumulation is unique for each subunit. The previously reported variation in amount of a' and a subunits in axis and cotyledons is also reflected in the amount of subunit specific mRNA which is present in each tissne. The ,B subunit, previously undetected in soybean axes, is found to be synthesized but rapidly degraded. These differences in 6-conglycinin protein accumulation may be reflected by the morphological differences observed in protein bodies between these two tissues.Biosynthesis ofthe ,B-conglycinins, the 7S seed storage proteins of soybean (Glycine max), has been the focus of recent research to study the mechanisms controlling the expression of specific genes during seed development (2, 3). f3-Conglycinin is a trimeric molecule of 180,000 to 240,000 D and is composed, primarily, of various combinations of the a', a, and # subunits (22), as well as lesser amounts of polypeptides related to a' and a-subunits that have been designated the y subunits (J Bryant, unpublished data). The a' and a subunits begin to accumulate soon after the cell division phase of seed development is completed (about 18 to 20 d after anthesis); the ,3 subunit accumulates 5 to 7 d later (8,17,21). The accumulation of j3-conglycinin mRNA molecules in seed was found to increase just prior to that of the protein subunits (9, 17). In the study by Meinke et al. (17), it was reported that while the a' subunit of ,-conglycinin is present in equal amounts in the embryonic axes and the cotyledons, the amount of a subunit is reduced and the ,B subunit is absent in axis tissue. These results indicated tissue specific as well as temporal regulation ofthe accumulation ofthe 7S storage protein subunits.

The maturation of pseudorabies virus DNA from the replicative concatemeric form to molecules of genome length was examined using nine DNA' temperaturesensitive mutants of pseudorabies virus, each belonging to a different complementation group. At the nonpermissive temperature, cells infected with each of the mutants synthesized concatemeric DNA. Cleavage of the concatemeric DNA to genome-length viral DNA was defective in all the DNA+ ts mutants tested, indicating that several viral gene products are involved in the DNA maturation process. In none of the ts mutant-infected cells were capsids with electron-dense cores (containing DNA) formed. Empty capsids with electron-translucent cores were, however, formed in cells infected with six of the nine temperature-sensitive mutants; in cells infected with three of the mutants, no capsid assembly occurred. Because these three mutants are deficient both in maturation of DNA and in the assembly of viral capsids, we conclude that maturation of viral DNA is dependent upon the assembly of capsids. In cells infected with two of the mutants (tsN and tsIE13), normal maturation of viral DNA occurred after shiftdown of the cells to the permissive temperature in the presence of cycloheximide, indicating that the temperature-sensitive proteins involved in DNA maturation became functional after shiftdown. Furthermore, because cycloheximide reduces maturation of DNA in wild-type-infected cells but not in cells infected with these two mutants, we conclude that a protein(s) necessary for the maturation of concatemeric DNA, which is present in limiting amounts during the normal course of infection, accumulated in the mutant-infected cells at the nonpermissive temperature. Concomitant with cleavage of concatemeric DNA, full capsids with electron-dense cores appeared after shiftdown of tsN-infected cells to the permissive temperature, indicating that there may be a correlation between maturation of DNA and formation of full capsids. The number of empty and full capsids (containing electron-dense cores) present in tsN-infected cells incubated at the nonpermissive temperature, as well as after shiftdown to the permissive temperature in the presence of cycloheximide, was determined by electron microscopy and by sedimentation analysis in sucrose gradients. After shiftdown to the permissive temperature in the presence of cycloheximide, the number of empty capsids present in tsN-infected cells decreased with a concomitant accumulation of full capsids, indicating that empty capsids are precursors to full capsids.