Download Ribosomal Protein S7 Distinguishes Multicellular from Unicellular

03.01
Ribosomal Protein S7 Distinguishes Multicellular from
Unicellular Fungi
William Duax1, David Dziak1, Jamerdon Dean1, Alexander Merriman1
1
Hauptman-Woodward Medical Research Institute
We have been tracing species evolution via alignment of amino acids conserved in the
folded core of ribosomal proteins in 8500 species. Ribosomal protein (Rsp) S7 follows an
evolutionary pattern similar to that previously found in Rsps S9, S12, and S19 in which
sequence variation in a single position separates G+ from G- bacteria, and different
homologs of each Rsp are found in the ribosomes of mitochondria, chloroplast and
cytoplasm, and fungi have mitochondrial and cytosolic copies. The mitochondrial Rsps are
homologous with the corresponding Rsps in alpha-proteobacteria consistent with
biochemical evidence that an alpha-proteobacteria was the mitochondrial endosymbiont.
The cytosolic Rsps in fungi differ significantly in length from the mitochondrial copy and
are homologous in length and sequence with the corresponding Rsps in Metazoa and
Archaea. Despite these similarities with S9, S12, and S19, S7 differs significantly from
them in at least one way. Mitochondrial and cytosolic copies of 98% of Rsps S9, S12, and
S19 are found in all fungi. In contrast Rps S7 has two copies in unicellular fungi only. The
only copies of Rps S7 found in multicelllular fungi are not those found in mitochondria. Of
the ribosomal proteins of the S subunit that we have studied in detail this uncommon
property of S7 is shared by S3. Ribosomal proteins that are labeled S7 in 5000 bacteria
and S7 or S5 in 3000 eukaryotes have 60 residues whose identities are 70% conserved.
The majority of the 3000 S7/S5 Rsps in Eukaryotes can be separated into subsets on the
basis of amino acid variation in a single sequence position, in which mitochondrial,
chloroplastic, and cytosolic S7s have Y(9%), H(16%) , and R(71%), respectively. There are
correlated changes in specific residues of similar percent occupancy in a several other
sequence positions.