The interaction of non-histone chromosomal protein HMG1 with core histones in nucleosomes was studied via reconstitution and photochemical cross-linking. The results obtained indicated that photoaffinity-labeled HMG1 interacted in nucleosomes with histone H3. Similar experiments with peptides derived from HMG1 by V8 protease digestion allowed to identify N-terminal domain of HMG1 (peptide V3) as a binding region for histone H3 in nucleosomes.