Energy Filtered Transmission Electron Microscopy (EFTEM) has been used
to study nucleic acids localization in unstained thin sections of vir
us-infected cells. For this purpose, phosphorus maps (P-maps) have bee
n obtained by applying the N-windows Egerton model for background subt
raction from data acquired by a non-dedicated TEM Jeol 1200EXII equipp
ed with a post-column PEELS Gatan 666-9000 and a Gatan Image Filter (G
IF-100). To prevent possible errors in the evaluation of elemental map
s and thus incorrect nucleic acid localization, we have studied differ
ent regions of swine testis (ST) cells with similar. local density con
taining either high concentration of nucleic acids (condensed chromati
n and ribosomes) or a very low concentration (mitochondria). Special c
are was taken to optimize the sample preparation conditions to avoid a
s much as possible the traditional artifacts derived from this source.
Selection of the best set of pre-edge images for background fitting w
as also considered in order to produce ''true P-maps''. A new software
for interactive processing of images series has been applied to estim
ate this set. Multivariate Statistical Analysis was used as a filterin
g tool to separate the ''useful information'' present in the inelastic
image series (characteristic signal) from the ''non-useful informatio
n'' (noise and acquisition artifacts). The reconstitution of the origi
nal image series preserving mainly the useful information allowed the
computation of P-maps with improved signal-to-noise ratio (SNR). This
methodology has been applied to study the RNA content of maturation in
termediate coronavirus particles found inside infected cells. (C) 1998
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