The nucleocapsid protein (NC) of human immunodeficiency virus type 1 (HIV-1) is a small, highly basic nucleic acid (NA)-binding protein with two CCHC zinc-finger motifs. In this study, we report for the first time, to our knowledge, that thermal stressed HIV-1 NCp7 maintained NA-binding activity. About 41.3% of NCp7 remained soluble after incubated at 100 degrees C for 60 min, and heat-treated NCp7 maintained its abilities to bind to HIV-1 packaging signal (Psi) and the stem-loop 3 of the Psi. At high or very high degrees of sequence occupancy, NCp7 inhibited first-strand cDNA synthesis catalyzed by purified HIV-1 reverse transcriptase, and heat-treated NCp7 maintained the inhibition. Moreover, both EDTA-treated and H23K + H44K double mutant of NCp7 inhibited first-strand cDNA synthesis, demonstrating that the NA-binding activity of NCp7 at high NC:NA ratios is independent on its zinc-fingers. These results may benefit further investigations of the structural stability and function of NCp7 in viral replication. (C) 2020 Elsevier Inc. All rights reserved.