Total RNA was extracted using the Trizol® method according to
the instructions of Invitrogen Life Technologies. Seven hundred and
fifty microliters of a crude extract obtained from infected shrimp
(sample 1) or purified IMNV (sample 2) were placed in micro-tubes
containing 500 L of Trizol and left at room temperature for 10 min.
Two hundred microliters of chloroform were then added to each
tube and shaken vigorously for 15 s. The mixture was again left
at room temperature for 5 min and then centrifuged at 12,000
×g
at 4 ◦C for 15 min. RNA precipitation was performed by transferring
450 L of supernatant to a microtube containing 500 L of
isopropyl alcohol. The mixture was incubated at room temperature
for 15 min and centrifuged at 12,000
×
g at 4 ◦C for 15 min. The
precipitate was suspended in 1 mL of 75% ethanol, shaken gently
in a vortex and centrifuged at 6600 × g at 4 ◦C for 5 min. The supernatant
was discarded and the tubes were gently inverted and placed
on filter paper to dry. The precipitate was then dissolved in 50 L of
DEPC-treated water and stored at
−20 ◦C for later use. The extracted
RNA was quantified by spectrophotometry using wavelengths of
260 nm and 280 nm. The integrity of the RNA was assessed by electrophoresis
in 2% agarose using TAE as the running buffer. The gel
was then stained with ethidium bromide and bands were observed
through translumination of ultraviolet light.