Biomedical subjects
B Runnegar
Publications and source records attributed to B Runnegar.
Megascopic eukaryotic algae from the 2.1-billion-year-old negaunee iron-formation, Michigan.
Hundreds of specimens of spirally coiled, megascopic, carbonaceous fossils resembling Grypania spiralis (Walcott), have been found in the 2.1-billion-year-old Negaunee Iron-Formation at the Empire Mine, near Marquette, Michigan. This occurrence of Grypania is 700 million to 1000 million years older than fossils from previously known sites in Montana, China, and India. As Grypania appears to have been a photosynthetic alga, this discovery places the origin of organelle-bearing eukaryotic cells prior to 2.1 billion years ago.
Nucleic acid and protein clocks.
The use of pairwise comparisons of correctly aligned DNA and protein sequences for the measurement of time in historical biology remains a contentious matter. However, the limited success of some molecular evolutionary clocks provides a stimulus to attempt to improve their resolution by the judicious selection of sequences for ease of alignment, commonality of function, taxonomic breadth and appropriate rates of evolution. Existing algorithms for correcting observed distances for superimposed nucleotide substitutions or amino acid replacements appear adequate for the task, given the noise that results from the inherent variability of the process. Some possible approaches are illustrated through the use of gene and protein sequences of the large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase: an enzyme that is demonstrably homologous from purple bacteria to flowering plants.
Collagen gene construction and evolution.
Collagen genes appear to have been assembled by the tandem repetition of homologous primary (9 base pair), secondary (54 base pair), and tertiary (702 base pair) modules. In vertebrate interstitial collagen genes many of the secondary modules are separated by introns, but in invertebrate collagen genes the non-coding sequences lie near the ends of supposed tertiary modules and are therefore about 702 (54 X 13) base pairs apart. The genes for vertebrate interstitial collagens (types I-III) seem to have been constructed by the tandem repetition of five tertiary modules, three of which were subsequently shortened by internal deletions. This shortening of the gene resulted in the non-integral relationship between the period of the fibrils and the length of the molecules of vertebrate collagens, and was therefore responsible for the mechanical properties of the completed product. Comparisons of the amino acid sequences of various collagens indicate that the main types of collagen evolved about 800-900 million years ago, a date that agrees well with the fossil record of primitive Metazoa.
Derivation of the globins from type b cytochromes.
Similarities in the amino acid sequences of vertebrate and invertebrate globins, b5 and b2 cytochromes and chicken sulfite oxidase point to a common ancestry for all of these proteins. The distal heme ligand (histidine or its equivalent) is common to both sets of proteins, but the proximal histidine ligand of the cytochromes is replaced by another histidine residue in the globins. This explains why the heme is reversed between globins and b5 cytochromes. It seems likely that the genes for primitive globins contained three exons, the first two of which were derived from a cytochromelike DNA sequence. A model is presented to show how globins may have evolved from a pre-existing type b cytochrome; the complexity of the required changes is an indication that all globins are monophyletic.