Sequences coding for histone H3 and H4 of Neurospora crassa could be identified in genomic digests with the use of the corresponding genes from sea urchin and X. laevis as hybridization probes. A 2.6 kb HindIII-generated N. crassa DNA fragment, showing homology with the heterologous histone H3-gene probes was cloned in a charon 21A vector. Using DNA from this clone as a homologous hybridization probe a 6.9 kb SalI-generated DNA fragment was isolated which in addition to the histone H3-gene also contains the gene coding for histone H4. Several lines of evidence demonstrate the presence of only a single histone H3- as well as a single histone H4-gene in N. crassa. The two genes are physically linked on the genome. DNA sequencing of the N. crassa histone H3- and H4-genes confirmed their identity and, in addition, revealed the presence of one short intron (67 bp) within the coding sequence of the H3-gene and even two introns (68 and 69 bp) within the H4-gene. The amino acid sequences of the N. crassa histones H3 and H4, as deduced from the DNA sequences, and those of the corresponding yeast histones differ only at a few positions. Much larger sequence differences, however, are observed at the DNA level, reflecting a diverging codon usage in the two lower eukaryotes.

The genes encoding yeast ribosomal proteins rp28 and S16A are linked and occur duplicated in the yeast genome. In both gene pairs the genes are approximately 600 bp apart and are both transcribed in the same direction. Both ribosomal protein genes resemble other ribosomal protein genes studied so far in many structural aspects. The genes are interrupted by an intron near the 5'-end of their coding sequence. In addition the flanking regions contain several conserved sequence elements, which may function in transcription initiation and termination. In agreement with findings concerning other cloned yeast ribosomal protein genes, upstream homology blocks occur that may be involved in coordinate control of ribosomal protein gene transcription. The complete pattern of conserved and diverged sequences between the two duplicate gene pairs is presented.