Sentence:  The double-stranded insert and linearized vector are denatured, and the resulting single strands of DNA anneal with their overlapping ends and extend using each other as a template to form double-stranded circular plasmids with only two <WSD>nicks</WSD>, one on each single strand. [...] Lastly, the <WSD>nicks</WSD> are covalently closed upon transformation into "E. coli" using its natural repair processes. 
Meaning of the word marked with <WSD> tags:  One of the single-stranded DNA segments produced during nick translation.