TY - JOUR
T1 - Nonhistone proteins HMG1 and HMG2 unwind DNA double helix
AU - Javaherian, Kashayar
AU - Sadeghi, Mohamad
AU - Liu, Leroy F.
N1 - Funding Information:
HMG2 are known to have approximately *5fe*-heTix at neutral PH under moderate salt conditions (13, I*). The absence of salt appears to have a small effect on a-hel ix content of HMG] and HHG2 (13). However, the structure of HMG, as probed by circular dichroism in near ultraviolet region shows a conformat ional change as a result of salt introduction into the medium (I1*). HMG| andHMG2 proteins bind toDNA noncooperatively similar toRNase. This property isnotshared byHDproteins ofAlberts and coworkers asdescribed by Jensen and Von Hippel (16). Furthermore, like ribonuclease, HMG| and HMG2 do not change the circular dichroism spectrum of DNA in near ul trav iolet (1*) . Recently, by using sequential chromatography on double-stranded DNA and single-stranded DNA columns, it was shown that two proteins from HTC cells were bound preferably to single-stranded DNA. A number of criteria established them similar to HMG| and HMG2 of calf thymus (17)- ACKNOWLEDGEMENTS The authors would like to thank Prof. James C.Wang, Harvard University, In whose laboratory a part of this work was performed. This work was supported by grants from Ministry of Science of Iran and University of Tehran. LFL is the recipient of an American Cancer Society Postdoctoral fellowshlp.
PY - 1979/8/10
Y1 - 1979/8/10
N2 - In a previous communication we have shown that both HMG1 and HMG2 non-histone proteins change the DNA helical structure and the binding of HMG1 and HMG2 to DNA induces a net unwinding equivalent of DNA double helix (Javaherian, K., Liu, L. F. and Wang, J. C. (1978) Science, 199, 1345-1346). Employing melting absorption technique, we now show that in the presence of salt HMG1 and HMG2 destabilize DNA whereas in the absence of salt, they both stabilize DNA molecules. Consequently the folded structure of HMG must play an important role in melting DNA. Furthermore, by measuring topological winding number using competition unwinding experiments, we conclude that HMG1 has a higher affinity for a single-stranded DNA relative to double-stranded DNA. These results together suggest that HMG1 and HMG2 unwind DNA double helix by local denaturation of the DNA base pairs. The net unwinding angles have been measured to be 22° and 26° per molecule of HMG1 and HMG2 respectively.
AB - In a previous communication we have shown that both HMG1 and HMG2 non-histone proteins change the DNA helical structure and the binding of HMG1 and HMG2 to DNA induces a net unwinding equivalent of DNA double helix (Javaherian, K., Liu, L. F. and Wang, J. C. (1978) Science, 199, 1345-1346). Employing melting absorption technique, we now show that in the presence of salt HMG1 and HMG2 destabilize DNA whereas in the absence of salt, they both stabilize DNA molecules. Consequently the folded structure of HMG must play an important role in melting DNA. Furthermore, by measuring topological winding number using competition unwinding experiments, we conclude that HMG1 has a higher affinity for a single-stranded DNA relative to double-stranded DNA. These results together suggest that HMG1 and HMG2 unwind DNA double helix by local denaturation of the DNA base pairs. The net unwinding angles have been measured to be 22° and 26° per molecule of HMG1 and HMG2 respectively.
UR - http://www.scopus.com/inward/record.url?scp=0018787029&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0018787029&partnerID=8YFLogxK
U2 - 10.1093/nar/6.11.3569
DO - 10.1093/nar/6.11.3569
M3 - Article
C2 - 226939
AN - SCOPUS:0018787029
SN - 0305-1048
VL - 6
SP - 3569
EP - 3580
JO - Nucleic Acids Research
JF - Nucleic Acids Research
IS - 11
ER -