Abstract
When microinjected into the cytoplasm of cultured mammalian cells, non-histone chromosomal protein HMG1 migrates into the nucleus and binds to the chromatin. To define the features of the HMG1 molecule which are essential for this activity, fragments of HMG1 and chemically modified HMG1 molecules were injected into HeLa cells and the capacity of each of these probes to accumulate in the nucleus was measured by an autoradiographic technique. Fragments representing the C-terminal and central portions of HMG1 did not concentrate in the nucleus; a fragment which consisted of the N-terminal two-thirds of the molecule and which lacked the 41 consecutive aspartate and glutamate residues located near the C-terminal end of the molecule accumulated to about the same extent as intact HMG1. When the amino groups of HMG1 were chemically modified, there was a progressive loss in the ability of the protein to accumulate in the nucleus; derivatization of one-fourth of the total amino groups reduced the concentration of microinjected protein in the nucleus relative to that in the cytoplasm to one-half of the original value. In contrast, modification of one-fourth of the total carboxyl groups did not significantly affect the capacity of HMG1 to accumulate in the nucleus, although further modification resulted in decreased nuclear accumulation. Iodination of tyrosine residues was without effect and modification of the cysteine residues had only a modest effect on the ability of HMG1 to concentrate in the nucleus.
Highlights
When microinjected into the cytoplasm of cultured of various investigators using a variety of cell types have been mammaliancells,non-histonechromosomalprotein consistent; nuclear proteinsenterand accumulate in the
HMGl and chemicallymodified HMGl molecules were may bedramatic; when the non-histone chromosomalprotein injected into HeLa cells and the capacity of each of HMG1’ was introduced into the cytoplasm of bovine fibrothese probes to accumulate in the nucleus was measured by an autoradiographic technique
HMGl were chemicallymodified, there wasa progres- region of the polypeptide chain,a regionwhich has been sive loss in the abilityof the protein to accumulate in called the karyophilic sequence
Summary
To obtain C2 and C3, a cyanogen bromide digest of HMGl prepared as described under “Experimental Procedures” was c2 m mmm. Chromatographed on Bio-Gel P-10 at pH 9.2 to produce the pattern shown in Fig. 2 A. Identification of the major component of peaks C2 and C3 was made on the basis of the known cleavage sites for cyanogen bromide, the approximate size of the fragments as determinedfrom their electrophoretic mobilities on CETAB gels, and their amino acid compositions. The amino acid composition of the material in peak C1 did not match that of any of the fragments which would be expected to arise from cleavage of HMGl atmethi-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
