Localization of chromosomal protein HMG-1 in polytene chromosomes of Chironomus thummi.

Abstract

The distribution of accessible antigenic sites in the chromosomal protein high mobility group one (HMG-1) in Chironomus thummi polytene chromosomes is visualized by immunofluorescence . The results indicate that (a) HMG-1 is distributed in a distinct banding pattern along the entire length of the chromosomes; (b) the banding pattern obtained with fluorescent antibody does not strictly correspond to that observed by phase-contrast microscopy ; and (c) the amount of HMG-1 increases, and the fluorescent banding pattern changes, during the development of the organism . Our findings suggest that the protein may be involved in the modulation of the structure of selected loci in the chromosome .The nonhistone chromosomal proteins are an integral part of the eucaryotic genome . Although the function of these proteins is not well understood, there is evidence that some proteins belonging to this group are important in maintaining the structure (1, 36) and regulating the function (9, 35, 41) of chromatin and chromosomes. The difficulties in purifying homogeneous molecular species from this group of proteins are a major obstacle in elucidating their function. Chromosomal protein high mobility group one (HMG-1) is one of the few nonhistone proteins that has been purified to homogeneity (11). This protein is ubiquitous in its distribution, as it is found in several eucaryotic kingdoms (15,28,37,38,40). Sequence studies revealed that it is unusually rich in charged amino acid residues, and that the negatively and positively charged residues are clustered on the polypeptide chain (39) . The proteins bind to histones and DNA and can induce changes in the DNA helical structure (17,19,44). Evidence has been presented that this protein is associated with isolated nucleosomes (13) .Antisera, elicited by HMG-1 protein purified from calf thymus, cross react immunologically with HMG-1 derived from several species (33) . The antibodies bind to chromatin (4), allowing these antisera to serve as useful cytological tools to study the cellular function of this protein.In the present study, we investigate the distribution of protein HMG-1 in polytene chromosomes of Chironomus thummi. Polytene chromosomes have the same fundamental chromatin fiber structure as that present in all eucaryotic systems (43) . Their large size offers the advantage of amplification in studying the location of a particular chromosomal protein and in following structural alterations associated with functional changes in the genome. Antisera to RNA polymerase (18), nonhistone proteins (36), histones (5), and fluorescent concanavalin A (22) have already been successfully used for such studies. The present study is the first investigation on the chromosomal localization of a structurally defined nonhistone protein that has been detected in several eucaryotic kingdoms . Affinity-purified antibodies are used to demonstrate that Chironomus contains a protein that is indistinguishable from its homologue purified from calf thymus . Its organization in the chromosome...

Differential labelling of the vegetative primary nucleus of the marine green alga Acetabularia by lectins, anti-immunoglobulin-antibodies and antinuclear autoimmunosera.

“…lm-p) Glycosidic determinants obviously are a general part of the nuclear reserve. They are found in conjunction with nonhistone chromosomal proteins of the detergent-resistant nuclear matrix (nuclear frame work) or with proteins of the easily extractable chromatin, as well as with the nuclear pore lamina complex (Silver et al 1978, Zegarelli-Schmidt et al 1980, Kurth and Bustin 1981.…”

Microscopic imaging of cells

“…1985). Antibodies to DNA and DNA-associated proteins, DNA specific fluorophores, and labelled RNA have also been used to study DNA conformation and folding (Kurth & Bustin, 1981;Bauman et al 1981;Arndt-Jovin et al 1983;Zarling etal. 1984;Brigati etal.…”

Antigenic determinants of high mobility group chromosomal proteins 1 and 2

“…In lieu of functional assays specific antibodies can serve as tools to identify, quantitate, localize, and study the in vivo function or defined components in chromatin and chromosomes (Bustin, 1979). Antibodies elicited by HMG-1 can react with HMG-2 and bind to both interphase chromatin (Bustin et al, 1977) and polytene chromosomes (Kurth & Bustin, 1981). Immu-nofluorescence techniques used to study the cellular localization of the proteins yielded conflicting results: the proteins have been detected both in the nucleus and in the cytoplasm of various cells (Bustin & Neihart, 1979;Smith et al, 1978;Bhullar et al, 1981).…”