It is intended to provide a polynucleotide comprising a viral base sequence, the viral base sequence containing: a first base sequence encoding a viral replication protein, and a second base sequence encoding a viral movement protein, the second base sequence being located downstream of the first base sequence and having a linking site for linking with an exogenous base sequence encoding a polypeptide to be expressed, the linking site being located downstream of the second base sequence, the second base sequence being obtained by modifying with a base sequence in a native sequence derived from a virus by insertion, substitution, or addition. By using this, a vector containing a viral base sequence is constructed, and a protein is efficiently produced without worsening growth of a host cell containing the vector.