In the larval salivary glands of C. tentans, it is possible to visualize by electron microscopy how Balbiani ring (BR) pre-mRNA associates with proteins to form pre-mRNP particles, how these particles move to and through the nuclear pore, and how the BR RNA is engaged in the formation of giant polysomes in the cytoplasm. Here, we study C. tentans hrp36, an abundant protein in the BR particles, and establish that it is similar to the mammalian hnRNP A1. By immuno-electron microscopy it is demonstrated that hrp36 is added to BR RNA concomitant with transcription, remains in nucleoplasmic BR particles, and is translocated through the nuclear pore still associated with BR RNA. It appears in the giant BR RNA-containing polysomes, where it remains as an abundant protein in spite of ongoing translation.

New tissue consistent with PDL developed on the surface of dental implants after implantation. This proof-of-principal investigation demonstrates the application of ligament-anchored implants, which have potential advantages over osseointegrated oral implants.

Transcriptionally active Balbiani ring (BR) genes in the salivary glands of the dipteran Chironomus tentans were studied by immunoelectron microscopy to establish the distribution of spliceosome components along a specific pre‐messenger ribonucleoprotein (pre‐mRNP) fiber. The BR genes are 35‐40 kb in size with three introns close to the 5′ end and one close to the 3′ end; a very large middle portion lacks introns. As a rule the 5′ introns are spliced concomitant with transcription in the promoter proximal third of the gene, while the 3′ intron is spliced post‐transcriptionally. The BR genes with growing pre‐mRNPs were visualized in situ, while completed and released pre‐mRNPs were isolated from the nucleoplasm and studied unfolded on a grid surface. An anti‐snRNP antibody (Y12) bound mainly to the promoter proximal third of the BR gene (86%) and only to a minor extent to the middle and distal thirds (7 and 7% respectively). An antibody to an hnRNP protein reacted with the proximal, middle and distal regions to an increasing extent (17, 38 and 45% respectively), reflecting the increase in size of the growing transcription product. In the nucleoplasmic pre‐mRNP particle only one end of the RNP fiber was labeled by Y 12, presumably the 3′ end; the anti‐hnRNP antibody decorated the entire RNP fiber. Thus, the snRNPs do not associate along the whole pre‐mRNP fiber but rather bind to the 5′ and 3′ ends, i.e. the regions containing the introns. The results also imply that the spliceosomes both assemble and disassemble rapidly on the pre‐mRNP fiber.

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