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Infection of Samsun NN tobacco with tobacco mosaic virus (TMV) induces a number of host‐encoded, so‐called pathogenesis‐related (PR‐) proteins, which are found in the intercellular space of the leaf and are associated with induced resistance. By immunoprecipitation of their in vitro translation products we were able to detect the mRNAs corresponding to a number of PR‐proteins in TMV‐infected tobacco, but not in healthy plants. Analysis by the Northern blot technique using cloned cDNA of PR1‐mRNAs as probe showed that the mRNAs for the closely related proteins PR1a, 1b and 1c occur at a low level in healthy tobacco; upon TMV infection this level is increased >100‐fold. The PR1‐specific probe did not hybridize to mRNAs corresponding to other PR‐proteins. Sequencing of the 5′‐terminal region of PR1‐mRNAs showed that PR1‐proteins are derived from precursors by removal of an N‐terminal signal peptide of 30 amino acids.

A 9.2 kb segment of the maxi-circle of Trypanosoma brucei mitochondrial DNA contains the genes for cytochrome c oxidase subunits I and II (coxI and coxII) and seven Unassigned Reading Frames ("URFs"). The genes for coxI and coxII display considerable homology at the aminoacid level (38 and 25%, respectively) to the corresponding genes in fungal and mammalian mtDNA, the only striking point of divergence being an unusually high cysteine content (about 4.5%). The reading frame coding for cytochrome c oxidase subunit II is discontinuous: the C-terminal portion of about 40 aminoacids, is present in the DNA-sequence in a -1 reading frame with respect to the N-terminal moiety. URF5, 8 and 10, show a low but distinct homology (about 20%) to mammalian mitochondrial URF-1, 4 and 5, respectively. In URF5, the first AUG is found at codon 145, whereas extensive homology to mammalian URF-1 sequences occurs upstream of this position. The possibility exists that UUG can serve as an initiator codon. URF7 and URF9 have a highly unusual aminoacid composition and do not possess AUG or UUG initiator codons. These URFs probably do not have a protein-coding function. The segment does not contain conventional tRNA genes.

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