Abstract:
Surface proteinaceous fibrils, termed fimbriae, were first
identified on gram negative bacteria in the 1940s. Fungal fimbriae,
discovered some 25 years later, are found on members of all fungal
classes. In the present study, polyclonal antiserum raised against the
fimbrial proteins of U. vio/acea were used in order to identify
antigenically related proteins from Coprinus cinereus and
Schizophy//um commune. Two polypeptides with molecular masses of
37 and 39 kDa from C. cinereus were observed and confirm earlier
results. A single previously unidentified 50 kDa polypeptide in S.
commune crossreacted with the antiserum. The 50 kDa protein was
found to consist of 3 isoforms with isoelectric points ranging from 5.6
to 5.8.
A fimbrial cDNA derived from U. vio/acea was used to identify
DNA restriction fragments from C. cinereus and S. commune showing
homology to the fimbrial transcript of U. vio/acea. Heterologous
hybridization with this cDNA was used in order to screen a C. cinereus
genomic DNA library. A single clone, A2-3A, with a 14 kbp insert
showed strong homology to the pfim3-1 cDNA. The region of homology,
a 700 bp Xba I fragment, was subcloned into pUG19. This plasmid was
refered to as pXX8. DNA sequence determinations of pXX8 and adjacent
fragments from A2-3A suggested that the cloned DNA was a portion of
the rONA repeat encoding the small subunit rRNA.
DNA sequence analysis of pfim3-1 yielded an incomplete open
reading frame. The predicted amino acid sequence codes for a 206
amino acid, 22 kDa polypeptide which contains a domain similar to a
transmembrane domain from rat leukocyte antigen, GDS3. As well, an
untranslated 576 nucleotide domain showed 81 % homology to pXX8 and
830/0 homology to the 188 rRNA sequence of Ustilago maydis. This
sequence was found adjacent to a region of adenine-thymine base pairs
presumed to represent the polyadenylation sequence of the fimbrial
transcript. The size and extent of homology is sufficient to account for
the hybridization of pfim3-1 to rDNA. It is suggested that this domain
represents a completely novel regulatory domain within eukaryotes
that may enable the observed rapid regeneration of fimbriae in U.
violacea.
