Date of Award
Doctor of Philosophy (PhD)
Extracts of sporangiospores of Mucor racemosus contained RNA that readily hybridized with ('3)H polyuridylic acid. Prior to germination, this RNA was in a form sedimenting at <80S. Within 10 minutes after initiating germination, most of this RNA sedimented with polyribosomes and 80S monoribosomes. Particulate material from spore extracts bound to oligo dT -cellulose at high ionic strength and was assumed to contain messenger ribonucleoprotein particles (mRNP's). A portion of the mRNP's was released from the column by lowering the ionic strength. Other portions were eluted stepwise in buffer containing 50% and 90% formamide and in 0.1-N NaOH. Identical elution patterns were observed whether monitoring incorporated ('31)P-orthophosphate or L- ('32)S methionine, absorbance at 280 nm, or hybridization of ('3)H polyuridylic acid. mRNP's from the first two fractions were analyzed. A bimodal population of particles was detected in sedimentation velocity and sedimentation equilibrium centrifugation. Particles eluted at low ionic strength demonstrated a sedimentation coefficient distribution of 20S-to-80S, with a mean of 55S. Particles eluted in formamide demonstrated a sedimentation coefficient distribution of 20S-to-60S, with a mean of 40S. Particles eluted at low ionic strength displayed two peaks in CsCl centrifugation, with bouyant densities of 1.37 gm/cc and 1.59 gm/cc. Particles eluted in formamide displayed a single peak with a buoyant density of 1.61 gm/cc. Particles eluted at low ionic strength and centrifuged in metrizamide solution formed two bands having bouyant densities of 1.15 gm/cc and 1.30 gm/cc; formamide-eluted particles banded only at the higher density. Mucor 40S ribosomal subunits banded at 1.56 gm/cc and 1.28 gm/cc in CsCl and metrizamide solution respectively. Analysis of mRNP fractions by sodium dodecylsulfate-polyacrylamide gel electrophoresis characterized protein components of these particles which helped explain their biomodal sedimentation behaviour. Each mRNP fraction contained a unique spectrum of proteins not shared by ribosomes or soluble cell proteins. The formamide-eluted particles contained two proteins, whereas the particles eluted at low ionic strength possessed 12 proteins. A 24,000-dalton protein was the predominant form in both. The denser mRNP's were smaller and lacked proteins found in the larger less dense particles. The former had a protein/RNA ratio of 45/55; whereas the later possessed a value of 90/10. Messenger RNA extracted from the mRNP's sedimented between 8S-to-20S.
Chapman, Charles Patrick, "Characterization of Messenger Ribonucleoprotein Particles in Dormant Sporangiospores of the Fungus Mucor Racemosus (Messenger-Rna)." (1986). LSU Historical Dissertations and Theses. 4290.