The present invention is directed to recombinantly-modified adeno-associated virus (AAV) helper vectors that are capable of increasing the packaging efficiency of recombinantly-modified adeno-associated virus (rAAV) and their use to improve the packaging efficiency of such rAAV. The present invention is particularly directed to recombinantly-modified adeno-associated virus (AAV) helper vectors that have been further modified to replace (or augment) the P5 and/or P40 promoter sequences that are natively associated with the Rep proteins encoded by such rAAV with AAV P5 and/or P40 promoters that are associated with the Rep proteins of an rAAV of different serotype. The use of such substitute or additional promoter sequences causes increased production of recombinantly-modified adeno-associated virus.