Final answer:
The RecA protein plays an important role in recombination involving single stranded DNA or the linear end of a double stranded DNA.
Step-by-step explanation:
The protein that plays an important role in recombination involving either single stranded DNA or the linear end of a double stranded DNA is the RecA protein. This protein is responsible for catalyzing the strand exchange reaction during homologous recombination and helps to repair DNA breaks. The RecA protein binds to single-stranded DNA and promotes the invasion of this ssDNA into a homologous double-stranded DNA to form a D-loop structure.