SUMMARYThe complete amino acid sequence of the basic nuclear protein of bull spermatozoa has been established. The sequence was partially deduced by characterization of peptides isolated from thermolysine and chymotryptic digests of the reduced and Saminoethylated protein. The complete sequence of the first 37 residues was determined by Edman-Begg degradation (Sequenator) of the protein. The amino acid sequence of the last 8 residues was determined by manual Edman degradation of an octapeptide obtained on cleavage of the reduced and S-methylated protein with Nbromosuccinimide.The basic nuclear protein of bull spermatozoa contains 47 amino acid residues with alanine at the amino terminus and giutamine at the carboxyl terminus. The protein contains 24 arginine residues and 6 half-cystine residues. 19 of the arginine residues are in the middle of the molecule, arranged in three clusters of, respectively, 7, 6 and 6 residues. Of the 6 half-cystine residues 2 are present in the amino-terminal region and 2 in the carboxyl-terminal region of the molecule. The half-cystine residues are responsible for the cross-linking of the deoxyribonucleoprotein molecules which gives the mature sperm nucleus an unusual resistance towards chemical and mechanical damage.The complete amino acid sequence is : H2N-Ala-Arg-Tyr-Arg-(Cys )2-Leu-ThrHis-Ser-Gly-Ser-Arg-Cys-(Arg) 7-Cys-(Arg)6-Phe-Gly-(Arg)6-Val-Cys-Tyr-ThrVal-Ile-Arg-Cys-Thr-Arg-Gln.

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In vivo methylated precursors of ribosomal RNA in yeast have been characterized on acrylamide gels. The initial ribosomal precursor in the yeast nucleus is a 37s RNA component, which is processed to a nuclear 28s RNA. Both the 37s and the 28s RNA components are important constituents of the yeast nucleus. A possible 33s RNA intermediate has been observed. Newly formed 18s rRNA rapidly enters the cytoplasm, while newly formed 26s rRNA appears later. The 26s rRNA is most probably formed from the nuclear 28s RNA.