"Dust" on the Moon

Abstract

We have previously shown that the pilL, pilN, pilQ, pilS, pilU, and pilV genes of plasmid R64 encode outer membrane lipoprotein, secretin, cytoplasmic ATPase, major pilin, prepilin peptidase, and minor pilin, respectively, which are required for thin-pilus formation. In this work, we characterized the products of the remaining essential genes, pilK, pilM, pilO, pilP, pilR, and pilT, with regard to their localization and processing. Overexpression systems containing pilM, pilO, and pilP genes fused with N-terminal glutathione S-transferase (GST) or a His tag were constructed. Overproduced proteins were purified and used to raise specific antibodies. Localization of PilM, PilO, and PilP proteins was performed by Western blot analysis with anti-GST-PilM, anti-PilO, and anti-PilP antibodies, respectively. The pilK, pilR, and pilT products were produced with a C-terminal His tag and then detected by anti-His tag antibody. Subcellular fractionation experiments with Escherichia coli cells producing R64 thin pili revealed that PilK, PilM, and PilR are inner membrane proteins, and PilP and PilT are periplasmic proteins. PilO protein was localized to the outer membrane in the presence of other Pil proteins, whereas it was localized to the cytoplasm in the absence of these proteins. Furthermore, the cleavage site of PilP protein was determined by N-terminal amino acid sequencing of purified mature PilP protein. We predict that PilK, PilM, PilO, PilP, and PilT proteins function as the components of the pilin transport apparatus and thin-pilus basal body.

Plutonium-244, Supernova and Hot Atom Chemistry

“…Also, lunar ash flows induced by the great collisions may have contributed to this material, and of course collisions of objects, large and small, with the surface have mixed up the surface materials". The results obtained in the present work are in line with the scenario envisioned by Urey [36,38] three decades ago.…”

“…Their dark color may be due to carbonaceous material and this lends some support to the suggestion that large amounts of such material are present in the moon". He also stated [38] in 1966 that: "I believe that the great collisions must have produced much fragmented material and that this would become distributed in some wide but unpredictable pattern on the moon's surface. Also, lunar ash flows induced by the great collisions may have contributed to this material, and of course collisions of objects, large and small, with the surface have mixed up the surface materials".…”

“…Urey [34][35][36][37][38][39] published a series of articles concerning the origin and chemical composition of the Moon and some of the predictions which he made during the 1960's turned out to be remarkably accurate. He stated [36] in 1960 that: "The dark mountainous areas west of Copernicus are part of the radiating riges from the Imbrian collision.…”

Plutonium-244 in the Early Solar System

“…It seems that these results can best be explained in terms of the idea expressed by Urey [63,64] three decades ago that large quantities of carbonaceous chondrite-like materials exist on the moon. Lunar ash flows produced by collisions of objects, large and small, with the moon rocks may have mixed up the surface materials.…”