Samji: Influenza A: understanding the viral life cycle 159 55. Fujii Y, Goto H, Watanabe T, Yoshida T, Kawaoka Y. Selective incorporation of in- fluenza virus RNA segments into virions. Proc Natl Acad Sci USA. 2003;100(4):2002- 7. 56. Muramoto Y, Takada A, Fujii K, Noda T, Iwatsuki-Horimoto K, Watanabe S, et al. Hi- erarchy among viral RNA (vRNA) segments in their role in vRNA incorporation into in- fluenza A virions. J Virol. 2006;80(5):2318- 25. 57. Watanabe T, Watanabe S, Noda T, Fujii Y, Kawaoka Y. Exploitation of nucleic acid pack- aging signals to generate a novel influenza virus-based vector stably expressing two for- eign genes. J Virol. 2003;77(19):10575-83. 58. Liang Y, Hong Y, Parslow TG. cis-Acting packaging signals in the influenza virus PB1, PB2, and PA genomic RNA segments. J Virol. 2005;79(16):10348-55. 59. Fujii K, Fujii Y, Noda T, Muramoto Y, Watan- abe T, Takada A, et al. Importance of both the coding and the segment-specific noncoding regions of the influenza A virus NS segment for its efficient incorporation into virions. J Virol. 2005;79(6):3766-74. 60. Palese P, Tobita K, Ueda M, Compans RW. Characterization of temperature sensitive in- fluenza virus mutants defective in neu- raminidase. Virology. 1974;61(2):397-410.